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The ultrastructure of oral (buccopharyngeal) membrane formation and rupture in the chick embryo.

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THE ANATOMICAL RECORD 197: 441-470 (1980)
The Ultrastructure of Oral (Buccopharyngeal) Membrane
Formation and Rupture in the Chick Embryo
ROBERT E. WATERMAN AND GARY C. SCHOENWOLF
Department of Anatomy, University of New Mexico,School of Medicine, Albuquerque,
New Mexico 87131 (RB.W.,G.C.S.)
ABSTRACT
The ultrastructure of the oral (buccopharyngeal) membrane
was examined by transmission and scanning electron microscopy (SEMI from its
initial formation (stage 8) to its complete disappearance (stage 20) in the chick
embryo. Thinning of the oral membrane prior t o rupture occurs in large measure
by increased interdigitation between cells of the stomodeal ectoderm and foregut
endoderm coincident with a decrease in the width of the intervening extracellular
space. Large numbers of necrotic cells were not observed. Interdigitation of
ectodermal and endodermal cells makes it increasingly dif?icult t o discern two
discrete epithelia, and no evidence that one germ layer disappears prior to the
other was observed. Changes occurred in the fine structure of the extracellular
matrix during formation and rupture of the oral membrane, and the organization
of this material within the oral membrane differed from that in regions immediately lateral to it. Copious amounts of amorphous, flocculant (“lamina-like”)
material are present within the oral membrane a t all stages. The basal lamina
of the ectoderm exhibits small loops or folds at early stages. These decrease in
number as the basal lamina becomes discontinuous prior to establishment of
direct intercellular contact between cells of the ectoderm and endoderm across
the intervening extracellular compartment. Initial perforations of the oral
membrane are preceeded by clefts between cells on both sides of this structure,
and SEM observations suggest that cells of the oral membrane continue to
interdigitate, elongate, and change relative positions during the rupture process.
The oral (buccopharyngeal, pharyngeal, oropharyngeal) membrane is composed of a region of close apposition between stomodeal
ectoderm and foregut endoderm. It forms a
temporary barrier between the stomodeal cavity and the lumen of the foregut during early
embryonic development of apparently all vertebrates. The oral membrane thins and eventually ruptures to create a patent passage
between the external embryonic environment
and the cranial end of the developing digestive
tract. Rupture of the oral membrane is vital
to the survival of the individual, since an
opening from the external environment into
the gastrointestinal tract is required to meet
the organism’s eventual nutritional needs. An
opening into the pharynx is also essential for
respiration in those vertebrates, such as fish,
which possess internal gills but no internal
nares. The oral membrane is illustrated and
mentioned incidently in numerous descriptions of vertebrate cranial development, but
detailed information regarding its formation
0003-276X/80/1974-0441$05.00
1980 ALAN R. LISS, INC.
and demise is rare, and is usually found only
in histologic studies of adjacent structures
such as Rathke’s pouch, the prechordal region,
or the heart (Parker, 1917; Adelmann, 1922;
Davis, 1923, 1927; Schwind, 1928; Aasar,
1931; Brahms, 1932; Gilbert, 1934, 1935; Kerr,
1946; Gilbert, 1957; Blechschmidt, 1961; Hillman and Hillman, 1965; Hammond, 1974;
Betz and Jarskar, 1974; Fremont and Ferrand,
1978; Jacobson et al., 1979).
Intimate contact between ectoderm and endoderm in the region of the oral membrane
prior t o its disappearance presumably prevents the migration of mesenchymal cells
across the ventral midline, thus preventing a
situation which might preclude or interfere
All correspondence and reprint requests should be sent to: Robert
E. Waterman, Ph.D.,Department of Anatomy, The University of New
Mexico, School of Medicine, Albuquerque, NM 87131.
Gary Schoenwolfs present address is: Department of Anatomy,
University of Utah, College of Medicine, Salt Lake City, UT 84132
USA.
Fkceived November 15. 1979; accepted March 7, 1980.
441
442
R.E. WATERMAN
AND
with formation of a future mouth opening.
This applies to the mesodermal cells of the
prechordal plate and head process as well as
to neural crest cells which migrate into the
craniofacial region. The presence of the oral
membrane appears to create a physical barrier
which aids in directing the expansion of these
cell populations, as shown in the avian embryo
in which the migrations of mesodermal and
cranial neural crest cells are known in considerable detail (Johnston, 1966; Noden, 1973,
1975, 1978). This is particularly important
during migration of neural crest cells into the
mandibular and maxillary processes which
grow forward around the margins of the oral
membrane to enlarge the stomodeum, and
rupture of the oral membrane does not occur
until these processes a r e well developed.
Adhesion between the ectoderm and endoderm
of the oral membrane a t early stages may also
serve to “anchor” the cranial end of the foregut
as it elongates (Stalsberg and DeHaan, 1968).
Mechanisms responsible for the rupture and
eventual disappearance of the oral membrane
a r e largely unknown. An ultrastructural
study of the oral membrane in the hamster
embryo (Waterman, 1977) revealed that thinning of this structure prior to its rupture is
due in part to increased intermingling of ectodermal and endodermal cells accompanied
by apparent phagocytosis of intervening extracellular material, but evidence of extensive
cell death during initial perforation of the oral
membrane was not observed. Several histologic studies of the cranial regions of avian embryos suggest that sequential disappearance
of the epithelial layers forming the oral membrane may occur in some birds, although both
ectodermal (Rex, 1897; Nicolas and Weber,
1901) and endodermal (Manno, 1903) cells
have been reported to disappear initially.
The present study was undertaken to clarify, by means of techniques affording greater
resolution than the light microscopic procedures used previously, the morphologic changes
exhibited by components of the oral membrane
during development and rupture of this structure in the chick embryo.
MATERIALS AND METHODS
Several dozen fertile White Leghorn eggs
were incubated in a forced-draft incubator a t
38°C until embryos reached stages 8-21
(Hamburger and Hamilton, 1951). Eggs were
then opened into a finger bowl containing
warm 0.9% saline, and the blastoderms were
G.C. SCHOENWOLF
rapidly cut away from the yolk, washed in
fresh saline, and immediately fixed and processed for light or electron microscopy.
Processing for scanning electron microscopy
(SEMI
Blastoderms were immersed for 2 to 3 hours
in 2% glutaraldehyde in 0.1 M cacodylate
buffer a t pH 7.2 (Sabatini et al., 1963). Fixed
embryos were then dissected free of surrounding membranes, pooled according to their
stage of development, washed in several
changes of buffer, secondarily fixed with 0.1
M cacodylate buffered 1% osmium tetroxide
for 1 hour, dehydrated in a graded ethanol
series, and dried by the critical-point method
using liquid CO,. The oral membrane in more
advanced stages was exposed by carefully
cross-sectioning the pharyngeal region at the
level of the first pharyngeal groove with razor
blades prior to dehydration and critical-point
drying.
Dried embryos were affixed to aluminum
stubs with their ventral surface facing upwards by means of double-stick adhesive tape
and conductive silver paint. The ectoderm
covering the ventral surface of the head, including the ectodermal component of the oral
membrane, was removed in some younger
specimens by gently applying a small piece of
double adhesive cellophane tape to the apical
surface of the ectoderm and lifting it upwards.
The tape with the adhering ectoderm was then
inverted and mounted on the stub adjacent to
the remainder of the specimen to permit examination of complimentary surfaces. Some
samples were dissected by means of small
pieces of broken razor blades held by forceps
either prior to or following critical-point
drying. Specimens were then coated with a
thin layer of go1d:palladium (60:40) in a Hummer I sputter coater, and examined with an
ETEC Autoscan SEM operated a t 10 kV. Some
dried embryos were sequentially dissected
with adhesive tape; the exposed surfaces being
recoated with go1d:palladium and rephotographed prior to succeeding manipulations.
Stereopairs of micrographs were recorded at
a relative tilt angle of 10”.
Processing for light microscopy (LM) and
transmission electron microscopy (TEM)
Blastoderms were briefly immersed (approximately 30 seconds) in cold (4°C) cacodylate
buffered (0.1 M at pH 7.2) 2% glutaraldehyde
(plus 0.05% calcium chloride and 0.1 M su-
CHICK ORAL MEMBRANE
crose) while small blocks of tissue containing
the desired regions of the embryos were dissected out. These portions of the embryos were
then immediately fixed on ice for one hour
with a cacodylate buffered (0.1 M a t pH 7.2)
mixture containing a final concentration of
2% glutaraldehyde/l% osmium tetroxide (plus
0.05% calcium chloride). Dissected regions
were then dehydrated with ethanol, transferred to propylene oxide, and embedded in
Epon 812 (Luft, 1961). Thick (1Fm) and thin
(100 nm) sections were cut with diamond
knives. Thick sections were stained with
methylene blue/azure I1 (Richardson et al.,
1960) and mounted on glass slides for examination by light microscopy (LM).Thin sections
were supported on uncoated copper grids,
stained with uranyl acetate and lead citrate
(Reynolds, 1963), and examined with a Hitachi HS-7S TEM operated a t 50 kV.
OBSERVATIONS
Stages 8-9
At stage 8 (4 somite paris; 26-29 hr), the
foregut is a broad, flattened pouch, the roof of
which is in close proximity t o the ventral
surface of the neuroepithelium (Fig. 1).The
floor of the foregut is thickened near the
ventral midline and will form the endodermal
component of the oral membrane, although
the precise limits of the membrane are difficult t o establish at this early stage. A considerable extracellular space separates the endoderm of the floor of the foregut and the
ectoderm covering the ventral surface of the
head. The opposed basal surfaces of both ectoderm and endoderm are somewhat irregular
in the region of the presumptive oral membrane. The basal ends of some ectodermal cells
project toward the endoderm, appearing as
“peaks” in histological sections. The primary
mesenchyme is sparse in the cephalic region
a t this stage.
By stage 9 (7 somite paris; 29-33 hr), the
oral membrane consists of a rather precisely
delimited region of close approximation between the thickened endodermal floor of the
foregut and the ectoderm near the ventral
midline (Fig. 2). A large, relatively cell-free,
extracellular space exists immediately beneath the surface ectoderm on each side of the
head, causing a bulging of the ventrolateral
aspects of the cranium. The oral membrane
consequently forms the floor of a shallow midline depression along the ventral surface of
443
the head cranial to the reflection of the body
fold. This depression consitutes the beginning
of the stomodeum. The developing ventral
aortae appear as small capillaries subjacent to
the floor of the foregut just lateral to the oral
membrane. Neural crest cells have not yet
migrated extensively into the cranial region,
and mesenchymal cells are only slightly more
numerous than at stage 8. The tip of the
notochord consists of a poorly circumscribed
mass of cells wedged between the neuroepithelium and the roof of the foregut.
The ectoderm of the oral membrane is
slightly thicker than the ectoderm covering
the remainder of the ventrolateral aspects of
the head. The ectodermal cells of the oral
membrane are connected by small intercellular junctions a t both their apical and basal
ends, and the ectoderm is underlain by a
continuous basal lamina which is thrown a t
intervals into small folds or looping projections (Fig. 3a, b). Numerous patches of fibrillar and flocculent extracellular material are
associated with the extracellular surface of
the basal lamina. These are more prevalent
in regions where the basal lamina is folded
than in regions where it is flattened. A few
profiles of cellular processes are present in the
extracellular space between the ectoderm and
endoderm (Fig. 3c). Some of these come into
close proximity to the basal lamina and associated flocculent material beneath the ectoderm, but direct cell-to-cell contact through
the basal lamina was not observed. The basal
surface of the endoderm of the oral membrane
is more irregular than that of the ectodermal
component. Cells of the foregut endoderm are
connected by small intercellular junctions a t
their apical ends facing the lumen of the
foregut, but the basal ends of the endodermal
cells in the oral membrane are more widely
separated (Fig. 3a). There is no continuous
basal lamina beneath the endoderm, but small
patches of electron dense, flocculent material
are associated with the basal surfaces of many
endodermal cells.
The apical surfaces of the ectodermal cells
covering the ventral aspects of the head a t
these stages exhibit no discernible regional
differences in surface topography when viewed
with the SEM (Fig. 4). Removal of the ectoderm exposes the basal surface of the thickened endoderm in the region of the developing
oral membrane as well as the mesenchymal
cells surrounding the foregut (Fig. 5). The
basal aspects of the loosely organized endod-
444
R.E. WATERMAN
AND
G.C. SCHOENWOLF
Fig. 1. Cross section through the cranial region of a stage 8 chick embryo. The thickened floor of the
foregut in the ventral midline, together with the overlying ectoderm, will form the oral membrane, although
this structure is not clearly delimited at this stage. The ectoderm and endoderm of the presumptive oral
membrane are separated by a distinct intercellular space. The neural folds are unfwed, and few mesenchymal
cells are present at this level. x 102.
Fig. 2. Cross section of a stage 9 embryo at the level of the mesencephalon. The neural folds are
approximated, but neural crest cells have not yet begun to migrate into the large, cell-free extracellular spaces
(*) at the lateral and ventral sides of the head. The oral membrane is now recognizable as an area of close
approximation between the thickened endodermal floor of the foregut and overlying ectoderm separated by a
narrow extracellular space. The oral membrane forms the floor of the developing stomodeum. x 107.
Fig. 3a-c. The ultrastructure of the apposed basal surfaces of endoderm and ectoderm in the oral membrane
at stage 9 is illustrated in a section nearly adjacent to that in Figure 2. (3a) The basal lamina underlying the
ectoderm is associated with accumulations of fibrillar and flocculent extracellular material, and exhibits small
folds or “pleats” at various intervals. Small patches of fibrillar extracellular material are associated with the
basal ends of many endodermal cells (arrows), but a continuous basal lamina is absent beneath the endoderm.
x 8,684. (3b) A portion of the basal lamina and associated extracellular material from the region indicated by
the asterisk in Fig. 3a is seen at higher magnification. X 23,827. (3c) A cell process (arrow) within the
extracellular space of the oral membrane is associated with a patch of extracellular material. x 10,085.
CHICK ORAL MEMBRANE
445
446
R.E. WATERMAN
AND
G.C. SCHOENWOLF
Fig. 4. Stereopair of scanning electron micrographs illustrating ventral aspect of cranial region
of stage 8+ embryo. The anterior end of the neural groove, reflection of the body fold (cut), and
anterior intestinal portal are seen. (This, and all subsequent stereopairs, are mounted for viewing
with stereoscopic glasses.) x 249.
Fig. 5. Stereopair of the same stage 8+ embryo shown in Figure 4, but with ectoderm removed
from the ventral surface of the head to reveal the basal surface of the foregut and associated
mesenchyme. The basal surface of the endodenn in the region of the presumptive oral membrane
(arrow) is not as flattened as that more caudally (*) at the level of the pericardial ccelom and dorsal
mesocardium. x 249.
Fig. 6. Stereopair of micrographs illustrating the morphology of the ventral surface of the
cranial region of a stage 11embryo. The cranial ends of the neural folds are approximated, but not
completely fused, in the region of the anterior neuropore. The lateral and ventral aspects of the
cranial region bulge outward caudal to the outlines of the laterally projecting optic vesicles. The
oral membrane (arrow) forms a portion of the floor of the forming stomodeum. A section of the oral
membrane in the region indicated by the arrow is shown in Figure 7. x 158.
CHICK ORAL MEMBRANE
447
448
R.E. WATERMAN AND G.C. SCHOENWOLF
ermal cells are connected by short strands
which probably represent both cellular processes and extracellular material. This is in
sharp contrast to the smoother basal surface
of the foregut lateral to the oral membrane.
Longitudinally oriented strands of flattened
cells on either side of the future oral membrane comprise the developing ventral aortae
which join the developing heart caudally.
lateral borders of adjacent endodermal cells.
The ectodermal cells remain attached by intercellular junctions a t both apical and basal
ends, but few small junctions are present between the basal ends of the endodermal cells.
It was not possible to further characterize
these embryonic junctions in the conventional
TEM preparations examined, although it appears that no desmosomes are present between
cells of either epithelium a t this stage.
When the ectoderm is carefully removed
from the ventral surfaces of dried specimens
and inverted, the extracellular material associated with its basal surface can be seen to
form strands which are aligned in the craniocaudal direction in the region of the oral
membrane (Figs. 12, 131, in contrast to the
more random organization of extracellular
material laterally (Fig. 13). Views of the complimentary endodermal surface reveal what
in stereopairs of micrographs appear to be
longitudinally oriented profiles of extracellular material, and fractured specimens indicate
that this material is interposed between the
basal ends of the endodermal cells of the oral
membrane (Fig. 14). The amount of aligned
material associated with both the ectoderm
and endoderm is most prominent near the
ventral midline.
With the ectoderm removed, the basal surface of the foregut in the midline between the
developing ventral aortae can be seen to differ
craniocaudally. Caudally, near the bifurcation
of the aortae and caudal to the oral membrane,
the endodermal cells are tightly compacted
and covered by a blanket of extracellular matrix (Fig. 12). More cranially, endodermal cells
within the oral membrane become increasingly rounded and separated. Short cellular processes connect adjacent endodermal cells of the
oral membrane and some extracellular material is present, but a uniform extracellular
coating is lacking.
Stages 10-1 1
At stage 10 (10 somite pairs; 33-38 hr), the
heart is beginning to loop to the right, the
optic vesicles are not yet constricted, and the
cranial flexure is beginning. By stage 11 (13
somite pairs-not
counting the first pair
which has dispersed; 40-45 hr), the heart is
bent prominently to the right and the bases of
the optic vesicles are constricted. The anterior
neuropore closes during these stages, although
complete union between all components of the
neural folds in this region is not complete
until stages 13-14 (Schoenwolf, 1979).
There is no clear indication of a demarcation
on the ventral surface of the cranium between
the ectoderm of the oral membrane and that
which will become Rathke’s pouch (Fig. 6),
and no striking differences in the apical morphology of the ectodermal cells of the oral
membrane relative to that of the ectodermal
cells lateral to the oral membrane were observed by SEM. The appearance of the oral
membrane in histologic sections is similar to
that a t previous stages, except for an increase
in the amount of extracellular material between ectoderm and endoderm. Strands of
material visible even with the light microscope extend between the irregular basal surfaces of endodenn and ectoderm (Fig. 7).
The basal lamina of the ectoderm of the oral
membrane is extensively folded or pleated and
is associated with accumulations of flocculent
material (Figs. 8, 10, 11). This is in sharp
distinction to the continuous basal lamina
Stages 12-15
beneath the ectoderm lateral to the oral membrane, which does not exhibit prominent folds
As development proceeds, the endoderm and
and is associated primarily with small round- ectoderm of the oral membrane become ined profiles termed “interstitial bodies” by Low creasingly apposed. By stage 13 (19 somite
(1970) (Fig. 9). A basal lamina is forming pairs; 48-52 hr), the cranial and cervical flexalong the dorsal and lateral walls of the fore- ures are broad curves and the head is turning
gut, but is largely discontinuous in the region onto its left side. Migrating cranial neural
of the oral membrane. Patches of flocculent crest cells have reached the lateral margins of
material are numerous within the oral mem- the oral membrane (Fig. 15). Rathke’s pouch
brane, where they are located primarily a t the appears as a small depression caudal to the
basal surfaces of the endodermal cells (Fig. closing anterior neuropore a t about stage 14
10).Similar material is only occasionally pres- (22 somite pairs; 50-53 hr), and the ectoderm
ent in the intercellular spaces between the near the midline caudal to Rathke’s pouch and
CHICK ORAL MEMBRANE
cranial to the small mandibular processes may
now be recognized as belonging exclusively to
the oral membrane.
The extracellular space between the endoderm and ectoderm of the oral membrane contains numerous profiles of cellular processes
and copious amounts of fibrillar and flocculent
extracellular material at stage 13 (Fig. 16).
Some extracellular fibrils exhibit the characteristic striated appearance of collagen (Fig.
17). The basal lamina of the ectoderm no
longer displays folds or pleats, and instead
exhibits occasional discontinuities which in
some places are associated with wide gaps
between the bases of the overlying ectodermal
cells (Fig. 16). The basal contour of the ectoderm is more irregular than in previous
stages, and appears more similar to that of
the endoderm. Profiles of basal lamina are
present along the basal surfaces of some endodermal cells, but a continuous basal lamina
is still not observed beneath the endoderm.
By stage 14, direct cell-to-cell contact between ectodermal and endodermal cells has
progressed to a point where extensive regions
of close apposition between cells are seen (Fig.
18). The intervening extracellular space is
obliterated a t such points. Interdigitation between ectodermal and endodermal cells makes
it difficult to discern the germ-layer origin of
some cells within the oral membrane. Dense
bodies are present, but never numerous, in
some cells e s p e c i a l l y those clearly recognizable as endodermal.
Increases in the degree of cranial flexure
and continued forward growth of the mandibular processes transform the originally flat
oral membrane into a curved, largely bilaminar, epithelial structure lying between the
mandibular processes and the deepening
Rathke’s pouch by stage 15 (ca. 50-55 hr)
(Figs. 19, 21). The apical profiles of the ectoderm and endoderm of the oral membrane
appear similar when viewed with the SEM,
and many cells of both sides are elongated
transversely across the oral membrane (Fig.
23).
Stages 16-18
The cells of the oral membrane continue to
interdigitate, making it increasingly difficult
to identify two distinct epithelial layers in
sections (Fig. 22). Small holes appear in the
oral membrane at about stage 16 (ca. 51-56
hr). These gradually enlarge during stages 17
(ca. 52-64 hr) and 18 (ca. 3 days) (Figs. 20,
24, 25). The initial perforations often form
449
near the lateral margins of the oral membrane
(Fig. 25), but a constant pattern of rupture
was not detected. The early perforations appear to be slit-like openings between adjacent
cells, which may be preceeded by deep clefts
between cells on either surface of the oral
membrane. The appearance of the apical surface of both the ectoderm and endoderm becomes increasingly irregular. Regions of obvious cell lysis were not observed within the
oral membrane, although some debris of unknown origin was sometimes present.
As the gaps in the oral membrane enlarge,
the intervening strands become increasingly
thin (Figs. 26-28). Points along some strands
are eventually formed by a single cell or a
small number of cell processes (Fig. 28). The
intercellular boundaries between adjacent
cells of the strands are distinct and the cell
surfaces appear intact when viewed with the
SEM.
The cells of the oral membrane are tightly
organized in solid epithelial cords a t these
stages, showing little extracellular space between adjacent cells (Fig. 29). Some cells extend across the entire thickness of the oral
membrane (Fig. 30). The cross-sectional areas
of cellular profiles seen in thin sections become
increasingly heterogeneous. Many very small
profiles are seen, and presumably correspond
to very thin cellular processes observed with
the SEM (Fig. 35). Numerous junctions, including desmosomes and small focal junctions,
occur between cells of the oral membrane.
Junctions are present not only between adjacent cells of the same germ layer, but between
ectodenn and endoderm cells as well. Pools of
extracellular material associated with patches
of basal lamina beneath the surfaces of adjacent cells are present a t intervals within the
oral membrane as the extent of interdigitation
between ectodermal and endodermal cells increases (Figs. 29, 32,331. Some smaller aggregations of extracellular material are partially
encircled by cell processes and may be
undergoing phagocytosis. Some cells of the
oral membrane contain dense bodies resembling phagosomes, but these are not numerous.
At later stages of perforation, the bases of
the remaining strands of oral membrane are
primarily conical, while the center of the
strands becomes more attenuated (Figs. 31,
34, 36, 37). Small groups of cells are seen for
a time along the junction between ectoderm
and endoderm and presumably represent remnants of strands which have ruptured and
450
R.E. WATERMAN AND G.C. SCHOENWOLF
Fig. 7. Cross section of the oral membrane of a stage 11 embryo. The basal surface of the
endoderm (top) is more irregular than that of the ectcderm (bottom).The ultrastructure of a portion
of the oral membrane indicated by the rectangle is seen in Figure 8. x 312.
Fig. 8. A portion of the lateral aspect of the oral membrane indicated by the rectangle in Figure
7 is seen in this transmission electron micrograph of a nearly adjacent section. The basal surfaces
of the endodermal cells are not underlain by a continuous basal lamina. The basal lamina beneath
the ectoderm exhibits numerous folds or loops which project into the extracellular space and are
associated with a flocculent extracellular material. The morphology of the ectcdermal b a d lamina
within the oral membrane differs from that of the basal lamina beneath the ectoderm of the head
immediately lateral to the oral membrane (*I which does not exhibit numerous loops. x 14,442).
Fig. 9. Portion of the basal lamina and associated “interstitial bodies” (arrows) beneath the
edoderm lateral to the oral membrane at stage 11. x 16,867.
Fig. 10. A portion of the extracellular space and apposed basal surfaces of the ectoderm and
endoderm of the oral membrane illustrating the difference in extracellular materials associated
with these two epithelia at stage 11. Numerous patches of fibrillar and flocculent extracellular
material (*), hut no continuous basal lamina, are commonly located beneath the endodermal cells.
The basal lamina of the ectderm is folded and associated with similar flocculent extracellular
material. x 13,006.
Fig. 11. h p s or folds of edodermal basal lamina within oral membrane are shown at higher
magnification. x 39,509.
CHICK ORAL MEMBRANE
451
452
R.E. WATERMAN AND G.C. SCHOENWOLF
Fig. 12. Stereopair of micrographs of a stage 11 embryo. The ectodenn has been removed from
the ventral aspect of the head. The basal surfaces of the enddermal cells in the region of the oral
membrane (arrow) are irregular. The ventral aortae (*I are present at the lateral margins of the
oral membrane. x 249.
Fig. 13. Stereopair of micrographs illustrating the basal surface of the ectodem removed from
the stage 11 embryo shown in Figure 12. Extracellular material tends to be aligned craniocaudally
in the region of the oral membrane, particularly near the ventral midline (arrow). Strands of
fibrillar extracellular material are more randomly organized lateral to the oral membrane (toward
bottom of micrographs). X 839.
Fig. 14. A fracture through the oral membrane of a stage 11 embryo reveals linear arrays of
extracellular material (arrow) between the basal surfaces of the ectoderm and endoderm. x 2,177.
Fig. 15. One-micron section through the cranial region of a stage 13 embryo. Mesenchymal cells,
presumably of cranial neural crest origin, have migrated to the lateral aspect of the ventral aortae
(VA) and oral membrane on each side of the head. x 102.
CHICK ORAL MEMBRANE
453
454
R.E. WATERMAN A N D G.C. SCHOENWOLF
Fig. 16. Portion of the extracellular space within the oral membrane of a stage 13 embryo.
Discontinuities are now present in the basal lamina of the ectoderm (*I. Cell processes (arrows)
project into the extracellular space near points where the basal lamina is absent. Flocculent and
fibrillar material is present between the basal surfaces of the ectoderm and endoderm. The basal
lamina beneath the endoderm is discontinuous. X 12,880.
Fig. 17. Extracellular fibril exhibiting striation characteristic of collagen from the extracellular
space of the oral membrane from a stage 13 embryo. x 67,442.
Fig. 18. Portion of the extracellular space within the oral membrane of a stage 14 embryo. Direct
cellular contacts between cells of the e d e r m and endoderm are now present across the extracellular space (*). Basal laminae of both edoderm and endoderm are discontinuous. Cells of both
edoderm and endodem contain pleomorphic dense bodies characteristic of lysosomes or phagosomes
(arrows). x 11,586.
CHICK ORAL MEMBRANE
455
456
R.E. WATERMAN AND G.C. SCHOENWOLF
by components of the intervening extracellular matrix, particularly at early stages prior
to formation of direct intercellular junctions
between the apposed epithelia. The fibrillar
and flocculent materials observed within the
extracellular space of the oral membrane during this study may represent substances responsible for such adhesion. The fact that this
matrix does not permit mesenchymal cell migration, and failure of the extracellular space
within the oral membrane to expand at a time
when an increased extracellular space containing a hyaluronate-rich matrix forms lateral to it during neural crest migration (Pratt
et al., 19751, further suggest that the composition of the extracellular matrix of the oral
membrane may differ from that lateral to it.
The ultrastructural differences of these matrices observed during this study are at least
consistent with this suggestion, although, except for obviously striated collagen fibrils, the
DISCUSSION
composition of this material has not been
The histologic and ultrastructural features determined.
Folding of the basal lamina subjacent t o the
of oral membrane formation in the chick embryo are essentially identical to those previ- ectoderm of the oral membrane, and the cranously described in the hamster (Waterman, iocaudal alignment of extracellular material
1977). Thinning of the oral membrane prior within the oral membrane at early stages (ca.
to rupture, in both species, results from in- 9-11], were striking features not previously
creased interdigitation between cells of the reported. This coincides with a period of rapid
stomodeal ectoderm and foregut endoderm elongation of the foregut (Seidl and Steding,
coincident with a decrease in the width of the 19781, and may reflect mechanical alterations
intervening extracellular space. This in- caused by positional changes of the endodercreased cellular intermingling produces dis- ma1 cells during this elongation (Bellairs,
continuities in the extracellular compartment, 1953; Rosenquist, 1966). Details of the morand the resulting pools of extracellular mate- phogenetic movements resulting in formation
rial are apparently reduced in size, at least in of the foregut remain incompletely underpart, through phagocytosis of material by the stood, however. Folding or duplication of basal
cells of the oral membrane. As in the hamster, lamina material has also been described in
the interdigitation between ectodermal and regions where epithelial cells are undergoing
endodermal cells makes it increasingly diffi- a functional transformation or are losing their
cult to discern two discrete epithelia, and no integrity as an epithelium (Parakkal, 1969;
evidence that one germ layer degenerates Byskov, 1978; Yamada et al., 1978; Bride and
Gomot, 19781, and in certain pathologic conprior t o the other was observed.
A significant degree of adhesion between ditions in a variety of tissues and organs
ectoderm and endoderm in the region of the (Birks et al., 1959; Hay, 1970; Vrako, 1974;
oral membrane is often assumed, although McNutt, 1976). The presence of folded basal
direct evidence demonstrating this is lacking. lamina within the oral membrane may, thereIndirect evidence, such as the failure of ce- fore, reflect a functional change in the ectophalic mesoderm to migrate into the oral dermal cells during the initial stages of oral
membrane, or of cranial neural crest cells to membrane formation which in turn may be
penetrate across the ventral midline as they somehow related to the establishment of a
migrate around the foregut and enter the close association between ectoderm and endodpharyngeal arches and facial processes (John- erm.
A small region of pleated basal lamina beston, 1966; Noden, 1975, 19781, suggests the
existence of a strong local adhesion between neath the epiblast associated with increased
the epithelial components of the oral mem- amounts of flocculent extracellular material
brane. Such adhesion is presumably mediated has been described at the advancing margin
retracted laterally (Fig. 37). The irregular
contours and blebbing of some cells within
these clusters viewed with the SEM may represent cell lysis (Fig. 38). The portions of the
epithelial lining of the pharynx and oral cavity derived from endoderm and ectoderm blend
imperceptibly between such remnants, and
some cells at the bases of the attachments
may be incorporated into the wall of the oral
cavity. Large cellular masses are occasionally
present in the preoral gut (Seessel’s Pouch)
and may represent remnants of the oral membrane which were sloughed prior to fixation
or were trapped during specimen preparation.
Only a few strands of the oral membrane
are present in late stage 18 embryos (Fig. 371,
and they are largely absent by stage 19 (ca.
3-3% days). The oral membrane is completely
absent in stage 20 and older embryos (Fig.
39).
CHICK ORAL MEMBRANE
of the mesenchyme (“edge cells”)just distal to
the terminal sinus of the expanding area vasculosa of stage 12 chick embryos (Bellairs,
1963; Mayer and Packard, 1978). It was suggested (Mayer and Packard, 1978) that the
pleated basal lamina and associated extracellular material may participate in the adhesion
between the mesoderm of the area vasculosa
and the epiblast known to exist in this region
(Augustin 1970). The presence of glycosaminoglycans (GAG) in this same region has been
demonstrated histochemically (Mayer and
Packard, 19781, although the ultrastructural
localization of these components is not known.
The fine structure of the flocculent material
associated with the pleated basal lamina in
the area vasculosa is similar to that of extracellular material between the ectoderm and
endoderm of the oral membrane a t similar
stages in specimens fixed and processed under
similar conditions. It also resembles “laminalike” (Cohen and Hay, 1971) material containing glycoprotein (Manasek et al., 1973; Manasek, 1976) associated with the floor of the
foregut in the region of the dorsal mesocardium during early stages of cardiogenesis in
the chick (Shain et al., 1972; Johnson et al.,
1974). The SEM observations reported in the
present study suggest that a continuous band
of “lamina-like” material may exist beneath
the ventral midline of the foregut during
stages 9- 11,extending from the cardiac region
through the oral membrane. Making an analogy with the characterization of this material
in the developing heart, this material may be
composed in large part of glycoprotein, which
may serve a variety of functions, including
cellular adhesion. While the ultrastructure of
“lamina-like” material within the oral membrane may resemble that seen elsewhere, however, caution must be used in ascribing specific functions to extracellular material within
the oral membrane without confirming data.
The interdigitation of ectodermal and endcdermal cells within the oral membrane is
preceeded by the appearance of discontinuities
in the ectodermal basal lamina. These are
first observed about stage 13, and may result
from changes in the secretion, or possible
enzymatic digestion, of basal lamina material.
The basal lamina is largely secreted by its
associated epithelium (Kefalides, 1973; Briggaman and Wheeler, 1975). Its function as a
scaffold necessary for epithelial tissue differentiation has been stressed by Vracko (1974)
and by studies in which experimental removal
of the basal lamina results in changes in
457
epithelial morphology and loss of normal behavior (Banerjee et al., 1977). Breakdown or
absence of a basal lamina occurs during normal development in regions where cells are
migrating from an epithelium (Wakely and
England, 1977; Tosney, 1978; Meier, 19781,
and in several normal and experimental conditions allowing contact between epithelial
cell processes and extracellular matrix and/or
direct heterotypic cell contacts (Morgan, 1976;
Slavkin and Bringas, 1976; Peck et al., 1977;
Hardy et al., 1973, 1978). In all these instances, discontinuities in the basal lamina
are correlated with structural and functional
changes in the overlying epithelial cells.
Breakdown of basal laminae and contact between processes of apposed epithelia also occur
during obliteration of the optic fissure in the
developing hamster eye (Geeraets, 1976), and
may reflect a feature common to other examples of fusion between the basal surfaces of
localized regions, such as fusion between pharyngeal pouch endoderm and ectoderm of the
corresponding pharyngeal grooves or formation of the cloaca1 membrane a t the caudal
end of the embryo. However, while the histologic appearance of these regions resembles
that of the oral membrane, the ultrastructure
of these latter two interactions has not been
reported in any vertebrate species.
Subtle changes in the production of basal
lamina components may not have been detected by the methods of fixation used in this
study. Addition of compounds such as ruthenium red, alcian blue, and tannic acid to
fixative solutions has been shown to preserve
additional ultrastructurally detectable material associated with the lamina densa of the
basal lamina (LuR, 19761, a t least some of
which has been characterized as sulfated and
non-sulfated GAG by correlated isotope labeling and enzymatic digestion (Martinez-Palomo, 1970; Trelstad et al., 1974; Hay, 1978;
Sanders, 1979; Solursh et al., 1979). The observations that certain basal laminae may be
removed by exposure to enzymes which presumably digest GAG components (Banerjee et
al., 1977; Sanders, 1979; Solursh et al., 1979)
suggests that the observed alterations in the
basal laminae within the oral membrane may
reflect changes in associated GAG, although
the presence of GAG in the oral membrane
has not yet been examined. Degradation of
the basal lamina allowing direct contact between epithelial and mesenchymal cells during tooth formation in the rabbit has been
tentatively attributed to collagenase and/or
458
R.E. WATERMAN
AND
G.C. SCHOENWOLF
Fig. 19. Midsagittal section of a stage 15 embryo. The oral membrane separating the stomodeum
and foregut is thin, but intact. A portion of the oral membrane is enlarged in Figure 21. x 133.
Fig. 20. Midsagittal section of a stage 17 embryo. Gaps (*) are now present in the oral membrane.
A portion of an oral membrane at a similar stage is shown at higher magnification in Figure 22. x
139.
Fig. 21. Portion of the oral membrane of the stage 15 embryo shown in Figure 19. It is difficult
to differentiate between the edoderm and endoderm with certainty. x 727.
Fig. 22. A portion of the rupturing oral membrane from a stage 17 embryo. The intact region of
the oral membrane is thin, and the cells are compact, with little distinct extracellular space evident
at the light microscopic level. Gap in membrane (*I. x 727.
Fig. 23. (SEM) of the endodermal surface of the oral membrane of a stage 15 embryo. x 1,167.
Fig. 24. SEM of a stage 18 embryo fractured through the mandibular pmesses and rupturing
oral membrane interposed between Seessel’s pouch at the cranial end of the foregut and the
stomodeum and Rathke’s pouch. x 250.
Fig. 25. Stereopair of micrographs of fractured oral membrane from a stage 16 embryo showing
clefts between adjacent endodermal cells (arrows) of the oral membrane near its lateral margin.
Many endodermal cells exhibit a single short cilium near the center of the apical surface. X 1,496.
CHICK ORAL MEMBRANE
459
460
Fig. 26.-28
R.E. WATERMAN
AND
G.C. SCHOENWOLF
Progressive stages of rupture of the oral membrane.
Fig. 26. Oral membrane of a stage 17-18 embryo viewed fmm the ectdermal surface. The apical profiles of the
extodermal cells are heterogeneous. Several small gaps are present. The tips of the mandibular processes are visible
toward the right. x 752.
Fig. 27. Oral membrane of a stage 17-18 embryo with more numerous perforations than in embryo shown in Figure
26. Deep clefts are present between adjacent cells of intact regions. Many cells are elongated transversely across the oral
membrane. Some cells exhibit micmvilli; others have smooth surfaces. X 1,086.
Fig. 28. A portion of an oral membrane from a stage 18 embryo. Strands separating gaps are variable in size, some
apparently formed by processes of a single cell or a small number of cells. x 1,573.
CHICK ORAL MEMBRANE
461
462
R.E. WATERMAN AND G.C. SCHOENWOLF
Fig. 29. Portion of the oral membrane from a stage 17 embryo. Extensive areas of apposition between ectodermal and
endodermal cells are seen. Pools of extracellular materials (*) of variable sizes are present near the center of the oral
membrane. Profiles of cells vary greatly in size, with smaller ones often present near the apical surfaces (arrows). x
13,420).
Fig. 30. Portion of an intact oral membrane from a stage 17 embryo. The oral membrane is almost entirely cellular at
this point, with some cells extending across the entire width of this structure (*I. It is difficult to establish the germ-layer
origin of many cells. Distinct intercellular junctions are frequently observed. X 10,581.
CHICK ORAL MEMBRANE
463
464
R.E. WATERMAN AND G.C. SCHOENWOLF
Fig. 31. A stage 18 embryo sectioned between the first and second pharyngeal arches. The
endodermal surface of the rupturing oral membrane is viewed between the mandibular processes
(the tips of which were mechanically damaged during the dissection process). Nasal pit (NF').The
oral membrane is shown at higher magnification in Figure 34. x 49.
Fig. 32. Cells of the oral membrane from a stage 17 embryo near a perforation (*) appear similar
to those more distant from the perforation. A small pool of apparent extracellular material is seen
(arrow). x 11,727.
Fig. 33. Portion of a large accumulation of predominantly fibrillar extracellular material within
oral membrane of a stage 17 embryo. x 12,000.
Fig. 34. Stereopair of micrographs of the rupturing oral membrane of the stage 18 embryo
illustrated in Figure 31. The thin strand toward the left was presumably broken during preparation.
x 500.
CHICK ORAL MEMBRANE
465
466
R.E. WATERMAN
AND
G . C . SCHOENWOLF
Fig. 35. Stereopair of micrographs illustrating a thin cellular process (arrow) a t the surface of a strand of rupturing
oral membrane from a stage 18 embryo. ( X 1,785).
Fig. 36. Stereopair of micrographs illustrating strands of oral membrane from a stage 18 embryo. ( x 403)
Fig. 37. Stereopair of micrographs illustrating a terminal stage of rupture of the oral membrane in a stage 18 embryo.
A single strand is viewed from the foregut surface. Several clumps of cells (arrow) presumably representing lateral
attachments of ruptured strands are seen along the lateral wall of the oral opening. ( X 333)
Fig. 38. A small group of cells representing the lateral attachment of a strand of oral membrane and showing signs of
cellular necrosis is seen in a stage 18 embryo. ( x 1,406).
Fig. 39. Stage 20 embryo cut in the midsagittal plane. No evidence of the oral membrane is visible along the lateral
wall of the developing oral cavity. ( X 107).
CHICK ORAL MEMBRANE
467
468
R.E. WATERMAN A N D G.C. SCHOENWOLF
other protease activity (Sorgente et al., 1977),
but factors responsible for degradation of basal
lamina material in other systems, including
the oral membrane, are largely unknown.
The changes in shape and arrangement of
both the ectodermal and endodermal cells
prior to and during rupture of the oral membrane revealed by the SEM in the present
study suggest a possible mechanism for the
initiation of gaps in this structure. Many cells
of the oral membrane which originally exhibit
polygonal or rounded apical profiles, become
elongated transversely across the oral membrane a s it thins, and long, slender cell extensions are associated with strands of the oral
membrane a t advanced stages of its rupture
(Figs. 28, 31, 34-36). Portions of these extensions presumably account for some of the
small cellular profiles seen in thin sections,
although direct correlations between SEM and
TEM images of the same specimen were not
attempted. It is possible that a t least some of
the initial perforations in the oral membrane
may arise a s spaces between cells as they
interdigitate and reorient within the thinning
oral membrane-perhaps in a manner analogous to formation of the foramina secunda in
the interatrial septum of the chick heart (Hendrix and Morse, 1977; Morse and Hendrix,
1980).Slit-like perforations appear in the cranial end of the septum primum of the chick
heart on day 4 of incubation and enlarge to
create gaps separated by thin trabeculae of
septa1 tissue. The initial perforations appear
to be formed by processes of endocardial cells
which extend into the core of the septum to
join with similar cell processes from the opposite side, thereby creating slit-like perforations while at the same time maintaining the
integrity of the endocardial lining (Morse,
1979).
The following paradigm of oral membrane
formation and rupture is proposed based on
currently available evidence. Interactions between foregut endodenn and surface ectoderm
are mediated initially by extracellular matrical components. Circumstantial evidence suggests that a degree of adhesion exists between
ectoderm and endoderm which is perhaps mediated by GAG or glycoprotein materials. Except for ultrastructurally detectable striated
collagen fibrils, however, the biochemical
identity of such materials remains unknown.
Direct intercellular contacts and junctions are
subsequently established between cells of the
endodermal and ectodermal epithelia with
concomitant breakup of the initially continuous intervening extracellular compartment
into pools of variable size. The protrusion of
cellular processes through the basal lamina to
allow establishment of direct intercellular
contact across the extracellular space presumably reflects a functional change in the epithelial cells which may be related to the synthesis and/or maintenance of the basal lamina
or other components of the extracellular matrix.
Increased interdigitation of epithelial cells
results in thinning of the oral membrane.
Continuation of such cellular rearrangements,
perhaps combined with dissociation of certain
intercellular contacts, may create the small
perforations which initially appear in the oral
membrane. It is also possible that other mechanisms, such as focal cell death or rupture a t
sites near large accumulations of extracellular
materials, may play a role in perforation of
the oral membrane. The numbers of sections
and samples examined make i t unlikely that
this latter event occurs with great frequency,
and direct continuity between pools of extracellular material and the cavities of either the
stomodeum or foregut was not observed in this
study nor in the hamster (Waterman, 1977).
Since dispersal of such discharged material or
the absence of a complete series of serial thin
sections may have prevented detection of this
situation, however, the possibility that pools
of extracellular material may create weak
spots in the thinning oral membrane cannot
be entirely ruled out. The amount of extracellular material within the oral membrane may
be reduced by enzymatic degradation during
thinning and rupture of the oral membrane,
although the degree of reduction and whether
extracellular and/or intracellular degradation
occurs has not been determined. Dense intracytoplasmic bodies with ultrastructural features of lysosomes or phagocytic vacules can
be seen in cells of the chick oral membrane a t
this stage (Betz and Jarskar, 19741, but the
presence of lytic enzyme activity associated
with these organelles has not been reported.
The strands of oral membrane thin progressively as the gaps in the oral membrane enlarge, and eventually consist of a single, or a
small number of cell processes. These slender
strands may either break or separate as cell
junctions are broken, and the ends retract
laterally, where they may persist for a short
CHICK ORAL MEMBRANE
time. Some cells of these clumps may degenerate. Others may be incorporated into the
epithelial lining of the oral cavity.
ACKNOWLEDGMENTS
The authors wish to acknowledge the technical assistance of Judi DeLongo during this
study. Supported i n part by a g r a n t
(#lF32NS06055-01) from the NIH to Dr.
Schoenwolf. Dr. R. Waterman is a recipient of
United States Public Health Services Research Career Development Award No. DE
00013.
LITERATURE CITED
Aasar, Y.H. (1931) The history of the prochordal plate
in the rabbit. J . Anat., 66:17-45.
Adelmann, H.B. (1922) The significance of the prechordal plate: An interpretive study. Amer. J . Anta.,
31:55-91.
Augustin, J.M. (1970) Expansion of the area vasculosa
of the chick after removal of the ectoderm. J . Embryol.
exp. Morph., 24:5%180.
Banerp, S.D., RJ. Cohn, and MB. Bernfield (1977) Basal
lamina of embryonic salivary epithelia. Production by
the epithelium and mle in maintaining lobular morphology. J . Cell Biol., 73:445-463.
Bellairs, R. (1953) Studies on the development of the
foregut i n the chick blastoderm. 2. The morphogenetic
movements. J . Embryol. exp. Morph., 1~369-385.
Bellairs, R. (1963) Differentiation of the yolk sac of the
chick studies by electron microscopy. J . Embyrol. exp.
Morph., 11:201-225.
Betz, T.W., and R. Jarskar (1974) Chicken pars distalis
development. Cell Tiss. Res., 155:291-320.
Birks, R., B. Katz, and R. Miledi (1959) Dissociation of
the 'surface membrane complex' in atrophic muscle fibers. Nature, 184: 1507-1508.
Blechschmidt, E. (1961) The Stages of Human Development Before Birth. W.B. Saunders Co., Philadelphia, 684
PP.
Brahms, S. (1932) The development of the hypphysis of
the cat (Felis domestica). h e r . J . Anat., 50:251-282.
Bride, J., and L. Gomot (1978) Changes a t the ectomesodermal interface during development of the duck
preen gland. Cell Tiss. Res., 194: 141-149.
Briggaman, R.A., and C.E. Wheeler, J r . (1975) The epidermaldermal junction. J. Invest. Der., 65:"-84.
Byskov, A.G. (1978) The anatomy and ultrastructure of
the rete system in the fetal mouse ovary. Biol. Reprod.,
19:720-735.
Cohen, A.M., and E.D. Hay (1971) Secretion of collagen
by embryonic neuroepithelium a t the time of spinal cordsomite interaction. Devel. Biol., 26:57%605.
Davis, C.L. (1923) Description of a human embryo having twenty paired somites. Carn. Contrib. Embryol., No.
72,15; 1-51.
Davis, C.L. (1927) Development of the human heart
from its first appearance to the stage found in embryos
of twenty paired somites. Carn. Contrib. Embryol., No.
107,19:245-284.
Fremont, P.H., and R. Ferrand (1978) Quail Rathke's
pouch differentiation. An electron microscopic study.
469
Anat. Embryol., 153:23-36.
Geeraets, R. (1976) An electron microscopic study of the
closure of the optic fissure in the golden hamster. Am. J.
Anat., 145:411-432.
Gilbert, M.S. (1934) The development of the hypophysis:
Factors of influencing the formation of the pars neuralis
in the cat. Amer. J. Anat., 54:287-313.
Gilbert, M.S. (1934) Some factors influencing the early
development of the mammalian hypophysis. Anat. Red.,
62: 337-360.
Gilbert, P.W. (1957) The origin and development of the
human extrinsic ocular muscles. Carn. Inst. Wash. Publ.
246, Contrib. Embryol., 36:59-78.
Hamburger, V., and H.L. Hamilton (1951) A series of
normal stages in the development of the chick embryo. J .
Morph., 88;49-92.
Hammond. W.S. (1974) Early hypophysial
_ _ . . development
in the chick embryo. Am. J. h a t . , 141:303-316.
M y , MH., K.S. Sonstepard, and PR. Swemy (1973) Lght
and electron microscopic studies of the reprogramming
of epidermis and vibrissa follicles by excess vitamin A in
organ culture. In Vitro, 8 L 405.
Hardy, M.H., P.R. Sweeny, and C.G. Bellows (1978) The
effects of vitamin A on the epidermis of the fetal mouse
in organ culture-an ultrastructural study. J . Ultrastruct. Res., 64:246-260.
Hay, E.D. (1970) Regeneration of muscle in the amputated amphibian limb. In: Regeneration of Striated Muscle and Myogenesis. A. Muro, S.A. Shafig, and A.T.
Milhorat, eds. Excerpta Medica, Amsterdam, pp. 3-24.
Hay, E.D. (1978) Fine structure of embryonic matrices
and their relation to the cell surface in ruthenium redfixed tissues. Growth, 42:399-423.
Hendrix, M.J.C., and D.E. Morse (1977) Atrial septation.
I. Scanning electron microscopy in the chick. Devel. Biol.,
57:345-363.
Hillman, N.W., and R. Hillman 11965) Chick cephalogenesis. The normal development of the cephalic region
of stages 3 through 11 chick embryos. J . Morph.,
116:357-370.
Jacohson,A.G.,DM.Miyamoto,andS.-H.Mai
(1979) Rathkes
pouch morphogenesis in the chick embryo. J. Exp. Zool.,
207~351-366.
Johnson, R.C., R.J. Manasek, W.C. Vinson, and J.M. Seyer (1974) The biochemical and ultrastructural demonstration of collagen during early heart development.
Devel. Biol., 36:252-271.
Johnston, M.C. (1966) A radioautographic study of the
migration and fate of cranial neural crest cells in the
chick embryo. Anat. Rec., 156:143-156.
Kefalides, N.A. (1973) Structure and biosynthesis of
basement membranes. International Rev. Con. Tiss. Res.,
6r63-104.
Kerr, T. (1946) The development of the pituitary of the
laboratory mouse. Quart. J . Microsc. Sci., 87:3-29.
Low, F.N. (1970) Interstitial bodies in the early chick
embryo. Am. J . Anat., 128:45-56.
Luft, J.H. (1961) Improvements in epoxy resin embedding methods. J . Biophys. Biochem. Cytol., 9:409-415.
Luft, J.H. (1976) The structure and properties of the cell
surface coat. Int. Rev. Cytol., 45291-382.
Manasek, F.J. (1976) Glycoprotein synthesis and tissue
interactions during establishment of the functional embryonic chick heart. J . Molec. Cell. Card., 8:389-402.
Manasek, F.J., M. Reid, W. Vinson, T. Seyer, and R. Johnson (1973) Glycosaminoglycan synthesis by the early
embryonic chick heart. Devel. Biol., 35:332-348.
Manno, A. (1903) Sopra il mod0 onde si perfora e scompare la membrana Faringea negli embrioni di Pollo. Riec.
470
R.E. WATERMAN AND G.C. SCHOENWOLF
Lab. Anat. Norm. Univ. Rome, 9:233-243.
Martinez-Palomo, A. (1970) The surface coats of animal
cells. Int. Rev. Cytol., 29:29-75.
Mayer, B.W., Jr., and D.S. Packard, J r . (1978) A study
of the expansion of the chick area vasculosa. Devel. Biol.,
63:335-351.
McNutt, N.S. (1976) Ultrastructural comparison of the
interface between epithelium and stroma in basal cell
carcinoma and control human skin. Lab. Invest.,
35: 132-142.
Meier, S. (1978) Development of the embryonic chick
otic placode. 11. Electron microscopic analysis. Anat. Rec.,
191:459-478.
Morgan, P.R. (1976) The fate of the expected fusion zone
in rat fetuses with experimentally-induced cleft palatea n ultrastructural study. Devel. Biol., 51:225-240.
Morse, D.E. (1979) Light and transmission electron microscopy of foramina secunda formation in the chick
atrial septum. Anat. Rec., 193:628 (Abstract).
Morse, D.E., and M.J.C. Hendrix (1980) Atrial septation.
11. Formation of the foramina secunda in the chick. Devel.
Biol., (in press).
Nicolas, A,, and A. Weber (1901) Observations relatives
aux connexions de la poche do Rathke e t des cavities
premandibulaires chez les embryons de Canard. Bibliogr.
Anat., 9:4-8.
Noden, D.M. (1973) The migratory behavior of neural
crest cells. In: Oral Sensation and Perception Development in the Fetus and Infant. J.F. Bosma, ed. Fogarty
Intl. Center Proc. No. 21. U.S. Gov. Printing Office. Chap.
2, pp. 9-36.
Nbden, D.M. (1975) An analysis of the migratory behavior of avian cephalic neural crest cells. Devel. Biol.,
42:10&130.
Ncden, D.M. (1978) The control of avian cephalic neural
crest cytodifferentiation. I. Skeletal and connective tissues. Devel. Biol. 67:296312.
Parakkal, P.F. (1969) Ultrastructural changes of the
basal lamina during the hair growth cycle. J . Cell Biol.,
40:561-564.
Parker, K.M. (1917) The development of the hypophysis
cerebri, pre-oral gut, and related structures in the marsupialia. J. Anat., 51: 181-249.
Peck, G.L., P.M. Elias, and B. Wetzel (1977) Effects of
retinoic acid on embryonic chick skin. J. Invest. Der.,
69:463-476.
Pratt,RM., MA. Larsen,and M.C. Johnston (1975) Migration
of cranial neural crest cells in a cell-free hyaluronaterich matrix. Devel. Biol., 44:298-305.
Rex, H. (1897) Uber das mesoderm des vorderkopfes der
Ente. Arch. Mikrosc. Anat., 50:71-110.
Reynolds, E.S. (1963) The use of lead citrate a t high pH
as a n electron-opaque stain in electron microscopy. J .
Cell Biol., 17:208-212.
Riehardson,K.C.,L.J&,dEH.Finke
(1960) pnbedding
in epoxy resins for ultrathin sectioning in electron mi-
croscopy. Stain Technol., 35313-323.
Rosenquist, G.C. (1966) A radioautographic study of labeled grafts in the chick blastoderm. Development from
primitive-streak stages to stage 17. Carnegie Inst. Wash.
Publ. 262, Contrib. Embryol., 38:31-110.
Sabatini,
D.D.,
K.
Bensch,
and
R.J.
Barnett (1963) Cytochemistry and electron microscopy. The preservation of cellular ultrastructure and enzymatic activity by aldehyde fixation. J . Cell Biol.,
17: 19-58.
Sanders, E.J. (1979) Development of the basal lamina
and extracellular material in the early chick embryo.
Cell Tiss. Res., 198t527-537.
Schoenwolf, G.C. (1979) Observations on closure of the
neuropore in the chick embrp. Am. J. Anat., 155:445-466.
Schwind, J.L. (1928) The development of the hypophysis
cerebri of the albino rat. h e r . J. Anat., 41:295-319.
Seidl, W., and Steding, G. (1978) Topogenesis of the
anterior intestinal port. Microkinematographic investigations on chick embryos. Anat. Embryol., 155:37-45.
Shain, W.G., S.R. Hilfer, and V.G. Fonle (1972) Early
organogenesis of the embryonic chick thyroid. I. Morphology and biochemistry. Devel. Biol., 28r202-218.
Slavkin, H.G., and P. Bringas, J r . (1976) Epithelial-mesenchyma interactions during odontogenesis. IV. Morphological evidence for direct heterotypic cell-cell contacts. Devel. Biol., 50t428-442.
Solursh, M., M. Fisher, and C.T. Singley (1979) The
synthesis of hyaluronic acid by ectoderm during early
organogenesis in the chick embryo. Diff., 14:77-85.
Sorgente, N., A.G. Brownell, a d H.D. Slavkin (1977) Basal
lamina1 degradation: The identification of mammalianlike collagenase activity i n mesenchymallyderived matrix vesicles. Biochem. Biophys. Res. Comm. 74:448-454.
Stalsberg, H., and R.L. DeHaan (1968) Endodermal
movements during foregut formation in the chick embryo. Devel. Biol., 18: 19g215.
Tosney, K.W. (1978) The early migration of neural crest
cells in the trunk region of the avian embryo: An electron
microscopic study. Devel. Biol., 62:317-333.
l h l s t d , R.L., K. Hay&, and B.P. Toole (1974) Epithelial
collagens and glycwaminoglycans in the embryonic cornea. Macromolecular order and morphogenesis in the
basement membrane. J. Cell. Biol., 62:815-830.
Vracko, R. (1974) Basal lamina scaffold-anatomy and
significance for maintenance of orderly tissue structure.
Am. J . Path., 77:314346.
Wakely, J., and M.A. England (1977) Distribution of
mesoderm in the early chick embryo. J . Anat., 124:241
(Abstract).
Waterman, R.E. (1977) Ultrastructure of oral (buccopharyngeal) membrane formation and rupture in the
hamster. Devel. Biol., 58:219-229.
Yamada, T., J.N. Dumont, R. Moret, and J.P.
Brun (1978) Autophagy in dedifferentiating newt iris
epithelial cells in uitro. Differentiation, 11: 133-147.
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