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The early development of the membranous labyrinth in mammalian embryos with special reference to the endolymphatic duct and the utriculo-endolymphatic duct.

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Urpurtment of A n u t o m y , Northwestern University Mcdicul Scliool, Chicago
Several investigators have recently drawn attention to the
manner in which, in the adult mammalian ear, the apposed
epithelial walls of the utricle and of the endolymphatic duct
constitute ‘a valve-like’ fold which, in projecting into the
utricular cavity, guards an elliptical utriculo-endolymphatic
communication. The importance of this fold in shaping the
embryonic labyrinth has not, however, been appreciated ; yet
certain other associated folds-although less conspicuous and
no more essential-have been pointed to as the determining
features in the conversioii of the otocyst into a vesicle possessing the subdivisions seen in the adult. It is our present
purpose to consider the interrelations of the three folds, as
well as the part played by each. In addition, we shall discuss
the development of the specialized, and possibly functionally
important, folds in the endolymphatic duct.
The material for the general developmental study of thct
ear, of which the current report is one phase, consisted of
205 selected series of mammalian embryos from the Harvard
Coiitributioii 110. 198 f r o m the Anatomical Laboratory of Northwestern University Medical School. This study coiistitutes one aspect of an investigation
conducted under the auspices of the American Otological Society. Paper read
a t the New York City meetings of the American Associatiou of Anatomists,
February, 1932. (Aiiat. Rec., vol. 52, pp. 2-3.)
Embryological Collection, distributed among twelve species
as follows: seventy series of human embryos, from 2.4 to 74
mm. in (CR) length; twenty-six of the cat, 4.6 to 39 mm.;
five of the dog, 12.5 to 17 mm.; twenty-four of the rabbit, 3 to
33.8 mm. ; twelve of the guinea-pig, 3.5 to 30 mm. ; thirteen of
the rat, 4.4 to 24.8 mm. ; one of the bat, 13.4 mm. ; twenty-three
of the pig, 3.1 to 48 mm.; three of the calf, 14.2 to 25.2 mm.;
seventeen of the sheep, 2.8 to 48.4 mm.; two of the deer, 9.8
to 18.6 mm.; ten of the opossum, 7.5 to 26 mm. The series
of infant and of child were added from the collection at
Numerous tracings from these series were then prepared
with the Edinger projection apparatus, and the most favorable of these chosen f o r the figures.
I n a recent publication (Anson, '34) it was pointed out that
the otocyst becomes a n independent vesicle, freed from the
outer cctoderm, in the embryo of 4 mm. (CR length), although
the disrupted stalk of original connection remains as apposed protuberances of otocyst and epidermis, even in the
6.7-mm. embryo (op. cit., fig. 14). In the latter embryo, and
representing a further step in a process apparent at 6.3 mm.,
the vesicle definitely possesses the dorsomcdial projection
which is termed the endolymphatic appendage. This appendage is delimited from the vestibular part of the vesicle by a
downward directed crease or ledge, the development of which
is the first phase of a three-part process which coiiverts the
simple otic vesicle into one consisting of three communicating
chambers, namely, endolymphatic duct, utricle, and saccule.
The vertical or dorsal crease, which is the primary one in
order of appearance, is very evident in the 22.8-mm. human
embryo (fig. 1, a t arrow I) while the medial one (at arrow
11) is not a s pronounced; the lateral ledge-which like the
preceding is horizontal in plane-is also distinct (arrow 111).
These folds in the vesicles of 22- and 28-mm. sheep embryos,
were recognized by Roettcher (1869 a, figs. 11 and 12, Taf.
TI),but their further development was not followed. I t is to
Pigs. 1 to 7 Tracings of endolymphatic duct aud adjacent area of membranous
labyriiitll from human series. Figures 1 to 4 and 7, X 3 7 ; 6 and 6, X 25.
1, 22.8 ~ u m . ;2, 29 mm.; 3 4 , 40 mm.; 5, infant, 4 months; 6, child, 3 years;
7, 36 mm.,a.v., auditory vesicle; caps, cartilagiuous otic capsule; c.d., cochlear
duct ; cochl., coelilear p a r t of vesicle ; div., saccular diverticula; e.ap., endolympliatie appendage ; c d . , eiidolympliatic duct ; e.s., endolymphatic sac; ep., epidermis ; l.s.d., 1;rteral semicircular duct; m.t., medullary tube ; sac., saccule ;
s . s . ~ . superior
semicircular duct; st., stapes; utr., utricle ; vest., vestibular p a r t
of vesicle ;, utiiculo-cntlolympllatic duct; u.e.f., utricular fold ('valve) ;
v., blood vessels. * Rugae, iii taiigeiitial section. Numbered arrows designate
folds discussed in text
the encroachment of the last-formed, or lateral, ledge that the
separation of the saccule and utricle is largely owing, according to the opinions of some investigators ; thus, Streeter
( ’06-’07, p. 165), in describing the subdivision of the primitive vesicle (in embryos between 18 and 20 mm.) describes
the ingrowth of a horizontal partition which “ultimately
reaches back to the entrance of the endolymphatic duct,” and
“divides the orifice of that structure, thus affording it separate openings into the utricle and saccule” (see also Keibel,
’12, p. 267). To the lateral ledge Chatellier (’26) also drew
attention, and named it the utriculo-saccular partition (‘cloison inter-utriculo-sacculaire’). We would now point out that
initially the two horizontal ledges (lateral and medial) are
directed into the vesicle toward each other, and that they
are subsequently altered in position so that the medial shelf,
even in the 22.8-mm. embryo, is carried caudalward (fig. 1,
arrow 11) in relation to the lateral one (arrow 111)-a
change more pronounced in the 40-mm. embryo (figs. 3 and
4,arrows I1 and 111); in this migration small saccular diverticula are likewise involved (figs. 1 and 3 ) . The dorsal shelf
comes directly downward, at first toward the medial fold
(fig. 1, arrows I and 11, respectively) ; subsequently (29 mm.,
fig. 2) it turns somewhat lateralward and overrides the shelf
from the lateral wall (figs. 2 and 3, arrows I and 111,respectively). Thus, the widely communicating utricle, saccule, and
endolymphatic duct of the 22.8-mm. embryo (fig. 1) are
brought, a t the 40-mm. stage (fig. 4) into the definitive and
permanent relationship obtaining in the adult ear-one in
which the utricle does not communicate directly with the
saccule, but with the latter through two intermediaries, tlie
divergent utriculo-endolymphatic (or utricular ) and the
utriculo-saccular (or saccular) ducts ; both of which appear
as limbs of the endolymphatic duct and with it assume the
form conventionally described as Y-shaped. The medial
ledge o r shelf (fig. 4, arrow II), now carried ventralward,
marks the line of separation between the nltriculo-saccular
duct and the saccule itself. The dorsal fold remains a promi-
nent morphological feature, and in older series of the ear,
when sectioned in favorable plane, appears to project into
the utricle as an elongate shank (fig. 5 , infant; fig. 6, child).
To this fold, in the ear of a 183-mm. human fetus, Bast ('28)
directed attention, treating it as a particular structure, and
regarding it as discoverable only in fortunate series;2 its
position, he believed, indicated that the flap might, in narrowing or closing the orifice of the ultriculo-endolymphatic duct,
control sudden changes of pressure within the endolymphatic
system. Its form and its constancy of occurrence in man
were established by the investigations of Wilson and Anson
( '29, two publications; twelve cases), and in mammals generally by those of Hoffman and Bast ('30; eleven species)
and of Roberts ( '32; one species, sixty series).
The succession of changes in the development of the membranous labyrinth in other mammals is very similar t o that
observed in man. I n the 7-mm. embryo of the cat the dorsal
fold is well developed (fig. 8, arrow I), already marking off
the endolymphatic appendage, while the medial ledge is just
apparent; the former ledge is pronounced in embryos of
10.6 mm., 14 mm., and 15 mm. (figs. 9 to 11),3 the medial
one much less so. The lateral ledge, evident at 24.1 mm. (fig.
12, arrow 111),is approaching the medial fold (arrow 11);
in extending over its dorsal aspect, and remaining ventral t o
the utricular fold (arrow I),it is so situated as to subdivide
the opening of the endolymphatic duct into the two portions,
the upper one communicating with the utricle, the lower one
with the saccule-a process accomplished in the 32.6-mm. and
39-mm. stages (figs. 13 and 14). The medial ledge finally
attains a distinctly ventral position in relation to the lateral
The structure was figured earlier, but without being named, by Boettcher
(1869a, fig. 12, Taf. 2 ) , Wittmaack ('24, Abb. 3 ) , Portmaiin ('24, fig. 3 3 ) ,
Chatellier ('26, fig. 4), Kolmer ( ' 2 7 , Abb. 5 0 ) , Fischel ('29, Abb. 446), and
The plane of sectiou is most favorable i n the series represented i n figure 10;
the differing plane in the several frontal series accounts f o r the apparent discrepancy in size between labyrinths, t h a t in the 32.6-mm. embryo (fig. 13)
appearing smaller than that in the 14-mm. (fig. 1 0 ) .
one (compare figs. 1 2 and 14). The three folds are present
in the 12.5-mm. dog embryo (fig. IS), a stage developmentally
similar to the 14-mm. cat embryo (fig. lo), as they a r e likewise
in the 21-mm. embryo of the rabbit (fig. 1 9 ) ; in two older
rabbit embryos, of 25 mm. and 29 mm. (figs. 20 and 21) the
Figs. 8 t o 21. X 37. Cat: 8, 7 mm.; 9, 10.6 mm.; 10, 14 min.; 11, 15 mm.;
12, 24.1 mm.; 13, 32.6 mni.; 14-16, 39 mm.; 16, 3 1 mm. Guinea-pig: 17, 18.5
nim. Dog: 18, 12.5 mm. Rabbit: 19, 21 mm.; 20, 25 mm.; 21, 29 mm.
manner in which the lateral and dorsal folds approach each
other is again illustrated. I n pig embryos from 15 to 48 mm.
in length the same evolution occurs; a t 15 mm. (fig. 22) the
dorsal and the medial folds mark off the utriculo-endolymphatic duct; the second fold at 20 mm. (fig. 2 3 ) is deeper,
and the proximal extremity of ihe endolymphatic duct correspondingly more incurved; it is even more cnrwd in the 32-
Figs. 22 t o 33. X 37. Pig: 22, 15 niin.; 23, 20 mm.; 24, 32 mm.; 25, 48 mm.
E:tt: 26, 15.1 min.; 27, 20.5 inin.; 28, 22.8 nim.; 29, 21.8 m n ~ . Opossum:
80, 13 mm. Shecp: 31, 18 m m . ; 32, 25 mm.; 33, 34.2 mm.
mm. embryo (fig. 24), while toward it, and somewhat dorsal
to it, the lateral fold is pressing toward the orifice of the
endolymphatic duct, there to pass beneath, and, in the 48-mm.
embryo (fig. 251, to underlie, the medial fold, and thus to
convert a n originally wide, single, communication between
utricle and saccule (fig. 22) into two slender ducts, by which,
through the intermediation of a third (the endolymphatic
duct) the two main chambers remain in communication. The
initial step in the same process is seen in r a t embryos between
15.1 and 22.8 mm. (figs. 26, 27, and 28), while the whole succession may be found in sheep embryos of 18, 25, and 34.2 mm.
(figs. 31, 32, and 33), to the first of which the 13-mm. opossum
(fig. 30) corresponds ~ l o s e l y . ~
The endolymphatic duct does not remain a smooth-walled
tube a s it is found in the 22.8-mm. human embryo (fig. 1);
in the slightly older stage, 29 mm., the lining of the wall of
the tube in its proximal portion is rendered irregnlar by
the development of low rugae (fig. 2). I n the embryo of
40 mm. (figs. 3 and 4, a t asterisks) the rugosities arc taller,
and a r e likewise prominent in a slightly earlier stage, the
36-mm. embryo (fig. 7 ; folds here and in figs. 2, 3, and 4 cut
transversely to their long axes5) ; such folds were observed
in sixteen additional series of human embryos, in the 39-mm.
and the 31-mm. embryos of the cat (figs. 14 and 16, respectively), but not in the other mammals studied.6
' I n addition to the series from which sections are shown i n the figures (figs.
1 to 6, 8 to 14, 18 t o 28, 30 t o 33) the valve may be seen cut at advantageous
plane in the following: man, 32 mm.; eat, 12 mm.; dog, 17 mm.; rabbit, 33.8
mm.; rat, 24.8 mm.; pig, 10 mm.; sheep, 13 mm. and 12 mm. (ser. 648, 404,
2053, 239, 1797, 401, 1345, 1342, respectively).
The plaits or rugae, as models prepared from several of the embryological
beries prove, pass ill longitudinal direction within the duct.
'In addition t o the scries from wliich sections are shown i n figures 2, 3, 4, 7, 14,
and 16, the following series display the longitudinal folds i n the proximal portion
of the endolymphatic duct: man, 45 mm., 44.3 mm., 42 mm., 37 mm., 31 mm.,
30 mm., 29 mm., 27 mm., 23 mm., and 24 mm. (series 2128, 1611, 841, 820, 2043,
913, 914, 2248, 2042, 24, respectivrly). They are less well marked in the
following earlier stages: 23 mm. ( t w o series), 22.8 mm. (two series), 22 mm.
a i d 19.3 mni. (ser. 2045, 204G, 737, 871, 851, 1597, respectively) ; they are wanting in the cmbrjos of 19 mm., 17.5 mm., 16 mm., 15 mm., 14.5 mm., 14.1 mm., 12
mm. (ser. 819, 2155, 2095, 2051, 1003, 2156, 816, respectively) and in other still
younger stages.
The wall of the distal portion of the endolymphatic appendage, or, more specifically, of the saccus, is likewise rugose
in some of the embyological series studied; in the cat embryo
of 39 mm. (fig. 15) the dorsal wall, or roof, of the endolymphatic sac is rather deeply infolded, as is the corresponding
area in the 18.5-mm. embryo of the guinea-pig (fig. 1 7 ) , and
of the 21.8-mm. rat embryo (fig. 29) ;? rugae are not yet present in any of the human series examined.*
The rugae-proximal and distal-are, in primordial form,
the abundant ridges found in the ears of adult mammals.
Guild (’27 a ) described and figured them as seen in sections
of the ductus and saccus of the adult guinea-pig where they
possess a regionally specialized epithelium and a subjacent
‘ I n addition to the series from which sections a r e shown iii the figures (cat,
fig. 15; guinea-pig, fig. 17; rat, fig. 29) the following series of the cat display
the plicate invaginations i n the distal portioii of the eiidolymphatic duct: 39 mm.,
32.6 mm., 31 mm. (two series), 24 mm., 23.1 mm. aqd 19 mm. (series 368, 505,
527, 500, 467, 466, 1985, respectively). Such invaginatioils are waiitiiig in the
following series of the cat: 24.1 mm., 17 mm., 15.6 mm., 15 mm. (two series)
(ser. 468, 492, 1983, 436, 438, respectively), and in additional younger stages.
They are present i n the followiiig series of the rabbit: 33.8 mm., 29 mm., 25 mm.,
22 mm., 2 1 mm. (series 239, 172, 169, 237, 738, respectively) ; they are inconsiderable i n the 12.5-mm. embryo (series 160) and waiitiiig in the 10-mm. (series
155). They occur in the 30-mm. guinea-pig (series 1779), iu the rats of 24.4 mm.
(series 1708) and 22.8 mm. (series 1941), but are not yet present in the 20.5-mm.
embryo (series 1806). Slight distal irregularities are seen i n pig embryos of 48
mm., 36 mm., 32 mm., and 20 mm. (series 2041, 2087, 74, 542, respectively).
There are nolie i n the 25.2-mm. calf (series 1 6 8 8 ) ; there are slight ones in
48.4-mm. sheep (series 1696), b u t none in the sheep of 34.2 mm. (series 1692), o r
in earlier stages. They are preseiit i n the 26-mm. and 23.5-mm. opossum embryos (series 2077 and 2096, respectively).
* The remarkable similarity i n labyriiithiiie morphology i n mammalian embryos
militates, we believe, against Doctor Streeter’s criticism ( ’27) of the notion of
ground-plans i n aiiimal structure; resort to the use of schemata has uot been
necessary in illustratiug the developmental stages of the auditory vesicle in
mammals, siiiee our actual tracings of sections possess the simplicity of diagrams,
and display negligible departures from a form which could readily be selected
as ‘archetypal.’ The same opiiiioii was expressed by the present author (Anson,
’ 2 7 ) at the Nashville meeting of the American Association of Anatomists, f o r
which Doctor Streeter ’s paper constituted the presidential address ; the recurrence
of epidermal thiekeiiiiigs about the oral orifice, and of ‘lips,’ among the classes
of vertebrates was regarded as an evidence of homology within the limits of
Daiiforth’s definition of t h a t term (Anson, ’29).
vascular stroma ; to the vascularized processes, upon abundant experimental evidence, Guild ( ’27 b) ascribed the function of resorption of the endolymph. They were, as seen in
man, described by Sterzi ( ’lo), and much earlier, with admirable figures, by Boettcher (1869 a, fig. 22, Taf. IV, cat ; 1869 b,
Taf. viiic, adult cat and human newborn). That the projections in man are actually elongate plaits and not simply villuslike hummocks (as they appear in sections) has been shown
recently by means of wax reconstructions (Anson and Wilson, ’30).s
ANSON, B. J. 1927 The comparative aiiatomy of the lips and labial villi.
(Abstract.) Nashville meeting, Am. Assoc. Anat., Anat. Rec., vol.
35, pp. 2-3.
1929 The comparative anatomy of the lips and labial villi of
vertebrates. J. Morph. and Physiol., vol. 47, pp. 335-413.
ANSON,B. J., AND W. T. BLACK,JR. 1934 The early relation of the auditory
vesicle to the ectoderm i n human embryos. Anat. Rec., vol. 58, pp.
127-13 7.
ANSON,R. J., AND J. G. WILSON 1929 The utricular fold in the adult human
ear. Anat. Rec., vol. 43, pp. 251-255.
~1930 The endolymphatic duct system i n the 2-year-old child. (Abstract.) Charlottsville meeting, Am. Assoc. Anat. ; Anat. Rec., vol.
45, p. 205.
BAST,T. H. 1928 The utriculo-lymphatic valve. Anat. Rec., vol. 40, pp. 61-64.
A. 1869 a Ueber Entwickelung uiid Bau des Gehorlabyrinths nach
Untersuchungen a n Siiugethieren. Verh. d. Eais. Leop.-Carol. 8. Akad.
d. Naturforscher, Bd. 35, S. 1-203.
1869 h Ueber den Aquaeductus vestibuli bei Katzen uiid Menschen.
Arch. f. Anat. u. Physiol., Jahrg. 1869, S. 372-380.
CHATELLIER,H. P. 1926 Evolution embryologique de l’appareil endolymphatique e t du cloisonnement utriculo-sacculaire chez I’homme. Arch.
d ’anatomie, d ’histologie, e t d’embryologie, T. 5, pp. 49-83.
A. 1929 Lehrbuch der Eiitwicklung des Menschen. Wien.
GUILD,S. R. 1927 a Observations upon the structure and normal conutents of
the ductus and saccus endolymphaticus i n the guinea-pig (Cavia
cobaya). Am. J. Anat., vol. 39, pp. 1-56.
1927 b The circulation of the endolymph. Am. J. Anat., vol. 39,
pp. 57-81.
E. F., AND T. H. BAST 1930 A comparative study of the ‘utriculoendolymphatic valve’ i n some of the commoll mammals. Anat. Rec.,
v01. 46, pp. 333-347.
a From unpublished data, by Anson and Wilson, on the 2-year-old child; by
Nesselrod and Anson on the 3-year-old and the adult.
KEIBEL, F., AND F. P. MALL 1912 Manual of human embryology, vol. 11.
W. 1927 Gehororgan, i n Handbuch d. mikr. Anat. d. Menschen, Bd. 3,
T. 1, S. 250-456. Berlin.
G. 1924 Oreilles, i n Travaux scientifique d u Dr. Georges Portmann,
pp. 16-163. Bordeaux.
ROBERTS,J. T. 1932 On the utriculo-endolymphatic valve i n the albino rat.
Anat. Rec., vol. 53, pp. 255-264.
G. 1910 I1 saceo endolinfatico. Ricerche anatomiche ed embriologiche.
Gegenbauer’s morph. Jahrb., Bd. 39, S. 446-496.
G. L. 1906-1907 On the development of the membranous labyrinth
and the acoustic and facial nerves i n the human embryo. Am. J.
Anat., vol. 6, pp. 139-165.
1927 Archetypes and symbolism. Science, N.S., vol. 65, pp.
WILSON, J. G., AND B. J. ANSON 1929 The ‘utriculo-endolymphatic valve’
(Bast) in a 2-year-old child. Anat. Rec., vol. 43, pp. 145-153.
WITTMAACH,K. 1924 Eiitgegnung zu vorstehenden Bemerkungen Alexander8
iiber meine Besprechung der makroskopischen Anatomie der nervosen
Aiiteile des Gehororgans im Handbuch der Neurologie. Zeitschrift
fur Hals-, Nasen-, und Ohrenheilkunde, Bd. 9, S. 80-83.
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development, mammalia, labyrinth, membranous, endolymphaticus, embryo, references, utriculo, special, early, duct
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