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The early development of the aortic arches of the cat with especial reference to the presence of a fifth arch.

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THE EARLY DEVELOPMENT O F THE AORTIC ARCHES
O F T H E CAT, W I T H ESPECIAL REFERENCE
TO THE PRESENCE O F A FIFTH ARCH.
BY
CALVIN B. COULTER.
From the Laboratory of Compwative Anatomy, Princeton University.
WITH TWELVE
FIGuBEB.
Through the investigations of Rathke, Hochstetter, and others
the development of the aortic arches of the vertebrates in general
is very well understood. The existence in the mammals, however,
of a fifth aortic arch, lying between the systemic and pulmonic
arches, has been a matter of recent discussion, and the work on this
paper was begun with the view of investigating the conditions as
they are in the cat. Consideration will be given to the papers dealing with a fifth arch in the mammals when this arch is dealt with
in the following pages. An extensive general bibliography may be
found in Hertwig‘s “Handbuch” following Hochstetter’s article on
“Die Entwickelung des Blutgef bisssystems.”
The history of the arches in the cat was studied by means of
wax reconstructions made after the method of Born at enlargements
of sixty-six and forty diameters. Twenty-six embryos were examined, from 3.5 to 16 mm. in length, and sixteen reconstructed, of
which ten are reproduced here. The reconstructions represent casts
as it were of the lumina of t.he blood vessels and the cavity of the
pharynx, and do not indicate the thickness of the walls or the character of the glandular structures developed from the branchial
pouches. No attempt will be made to describe fully the development of the pouches, which are shown in the earlier stages to illustrate the consistent relations of the blood-vessels to the branchial
arches.
‘0.Hertwig, Handbuch der rergleichenden und experimentellen Entwicke
lungegeschichte der Wirbeltiere, Band 111, Teil 2.
(578)
Aortic Arches of the Cat.
570
LIST OF MATERIALSTUDIED.
3 mm.
3 mm.
4.5 mm.
5 mm.
5 mm.
5.6 mm.
6 mm.
6 mm.
6 mm.
6.5 mm.
5 mm.
5mm.
6.8 mm.
6.8 mm.
7 mm.
7 mm.
7 mm.
7.25 mm.
8 mm.
8 rnm.
9 mm.
10 mm.
11.5 mm.
Series 188.
Series 45.
Series 93.
Series 47.
Series 11.
Series 110.
Series 84.
Series 126.
Series 127.
Series 131.
Series 30.
Series 31.
Series 103.
Series 105.
Series 137.
Series 138.
Series 2.
Series 13.
Series 3.
Series 5a.
Series 19.
Series 101.
Series 29.
Columbia University Collection.
Princeton University Collection.
Columbia University Collection.
Princeton University Collection.
Princeton University Collection.
Columbia University Collection.
Columbia University Collection.
Columbia University Collection.
Columbia University Collection.
Columbia University Collection.
Princeton University Collection.
Princeton University Collection.
Columbia University Collection.
Columbia University Collection.
Columbia University Collection.
Columbia university Collection.
Princeton University Collection.
Princeton University Collection.
Princeton UniverGty Collection.
Princeton University Collectbn.
Princeton University Collection.
Columbia University Collection.
Princeton University Collection.
In the youngest embryo examined ( 3 m.,Fig. l), in which the
pharyngeal membrane has not yet broken through, there is a single
aortic arch, through which on each side the primitive heart communicates directly with the dorsal aorta. There are two well-defined
branchial pouches on each side, which appear to be homologous with
the first and second pouches of later stages. Between these two
there are slight protrusions from the dorsal aorta, and an irregular
outgrowth from the ventral aorta, as shown in Fig 1. This ventral
outgrowth is of a very indefinite character, and has the appearance
of a tissue-space which has become continuous with the ventral aorta
in two places. An identical condition was found in another embryo
of this litter, Series 188. Whether or not these cavities are to be
regarded as tissue-spaces that are utilized in forming the second
aortic arch cannot be discussed here; at any rate, they and the
dorsal buds seem to be the ventral and dorsal anlages of the second
arch. Behind the second pouch also there i 3 on each side an evagination from the dorsal aorta, the anlage of the third arch.
An embryo of 4.5 mm. (Fig. 2) shows the second and third arches
completed, and the ventral anlage of the fourth arch extending
caudad from the middle of the third arch. On the left side, a
580
Calvin 13. Coulter.
dorsal as well as a ventral anlage of the fourth arch has appeared.
From the distal end of the first arch a vessel has grown forward,
and when this arch degenerates carries the blood directly forward
from the dorsal aorta into the head region. This vessel constitutes
that portion of the internal carotid artery which is developed in
FIQ.1.-Reconstruction of the aortic arch system of a 3 mm. cnt embryo.
Series 45, Princeton University Collection. Right side. X 66.
Fro. 2.-Reconstruction of the aortic arches of a 4.5 mm. cnt embryo.
Serles 93, Columbla University Collection. Right side. x 50.
front of the first aortic arch. A small aortic bulb has been formed
by the coalescence of the ventral ends of the first and second aortic
arches. Behind the third arch a large branchial evagination has
made its appearance, and has already begun to divide into the third
pouch and the swelling from which the fourth and fifth pouches are
subsequently formed by a similar division.
Aortic Arches of the Cat.
581
In the next stage (5 mm., Fig. 3) the first two aortic arches are
reduced in size, and from the ventral portion of the first arch capillaries extend out into the mandibular region. The ventral ends of
the third arches have begun to fuse together, so that the aortic bulb
is enlarged and shifted caudad. This is a stage in the progressive
coalescence which takes place between the ventral ends of all the
aortic arches, with the subsequent formation of a large aortic bulb.
FIG.3.-Reconstruction of the aortic arches of a 5 rum. cat embryo. Series
47, Princeton University Collection. Right side. x 50.
The dorsal anlage of the fourth aortic arch is now present on both
sides, and the separation of pouches 3 and 4-5 more distinct.
Fig. 4,of an embryo 5 mm. in length, shows the fourth arch completed. The first arch has lost its connection with the dorsal aorta,
leaving a dorsal remnant which soon disappears. Just anterior to
this remnant, and to the hypophysis which lies mesial to it, there is
an anastomosis, not visible in the figure, between the two dorsal
aorta by means of a large cross-trunk, a peculiarity which was observed only in this embryo and in Series 31, another of the same
582
Calvin B. Coiilter.
litter. The fusion of the ventral ends of the third arches has continued and now involves the bases of the fourth aortic arches. I n
this embryo (Fig. 4) the sixth arch makes its first appearance, as a
spur extending caudsd from the ventral portion of the fourth arch.
The third pharyngeal pouch has become still farther separated from
Fro. 4.-Reconstructlon of the aortic arches of a 6 mm. cat embryo. Series
30, Princeton University Collection. Right side. X 60.
the evagination caudal to it, which is a simple rounded structure
that shows no evidence of division.
The 5 mm. embryo, Series 11 (Fig. 5 ) , is a very important one, for
it brings us to the question of a fifth aortic arch.2 Before presenting
the results obtained in the cat the observations in regard to this arch
in other mammals will be briefly reviewed.
I n view of the differences observed in the relative development of their
arches, it i s probable that the measurements of the 5 mm. embryos (Ser. 11,
30,and 31) are incorrect.
Aortic Arches of the Cat.
583
Zimmermann3 (1889) described in the rabbit an artery arising
from the truncus arteriosus and emptying into the dorsal aorta near
the base of the pulmonic arch, separated from the systemic and
pulmonic arches by distinct entodermal pouches. In an incomplete
sheep series he found a vessel extending ventrad from the distal end
of the pulmonic arch, but was unable to trace its ventral connection.
The fifth arch as he described it in man represented a very different
condition, as it arose from and terminated in the fourth arch, enclosing its middle third.
Tandlel." (1902) found in two human embryos a vessel extending
from the ventral aorta to the distal end of the pulmonic arch. In the
rat he interpreted an anastomosis between the fourth and pulmonic
arches as a fifth arch, but could not discover a fifth pouch.
Lehman6 (1905) found in the rabbit irregular vessels arising from
the fourth and pulmonic arches, and in the pig a somewhat similar
condition, but found in one case a complete vessel from the ventral
end of the fourth arch to the dorsal aorta. This vessel was connected by a short stem with the pulmonic arch, and was separated
from the fourth and sixth arches by distinct branchial pouches.
Lewise (1906) in the rabbit and pig described only irregular vessels, and expressed the belief that none of these spurs or additional
roots at the bases of the arches could be interpreted as a fifth aortic
arch, and that the evagination described as postbranchial body is not
serially homologous with the preceding pouches.
Lacy' (1906), commenting upon the condition of the fifth arch in
the mammals, states his belief in the existence of a fifth arch. He
W. Zimmermann. Ueber einen swischen Aorten und Pulmonalbogen
gelegeuen Kiemenarterienbogen beim Kaninchen. Anat. Am., Bd. IV, 1889.
Relionstruction einea menschlichen Embryos. Verh. Anat. Ges., 1889.
J. Zur Entmickelungsgeschichte der Kopfarterien bei den Mam4Tn~~cller,
malia. Xorph. Jahrb., Bd. 30, 1902.
'Lehiuniin, Harriet. On the Embryonic History of the Aortic Arches in
Mamuials. Anat. Am., Bd. XXVI, 1905.
*Lewis, F. T. The Fifth and Sixth Aortic Arches and the Related Pharyngeal Pouches in the Rabbit and Pig. Anat. Am., Bd. XXVIII, 1906.
'Locy, William A. The Fifth and Sixth Aortic Arches of Chick Embryos
with comments on the condition of the same vessels in other Vertebrates.
Anat. Am., Bd. S S I X , 1906.
584
Calvin B. Coulter.
thinks that its extreme variability and transitory character undoubtedly explain the lack of definite information regarding it in some
of the forms, and notes the individual differences in those forms in
which a complete arch has been described.
Souli6 and Bonnes (1908) in their paper on the arches of the
mole describe a typical fifth aortic arch, arising separately from the
FIQ.5.-Reconstruction
of the nortic arches of a 5 mm. cat embryo. - Series
11, Princeton University Collection. Right side.
x
50.
aortic bulb or in a common trunk with the pulmonic, and emptying
in every case into the dorsal aorta in common with the pulmonic
arch. This B t h vessel in the mole occupies a distinct branchial
arch, which lies somewhat lateral to the fourth and sixth arches.
The typical mammalian fifth aortic arch appears thus to be a
vessel which arises from the aortic bulb and empties into the pulmonic
arch near its junction with the dorsal aorta. The development is
‘Souli6, A.. and Bonne, C. L’Appareil Branchial et les Arcs Aortiques de
I’Embryon de Taupe. Journ. de 1’Anat. et de In Phys., No. 1, 1908.
Aortic Arches of the Cat.
585
most complete in man and the mole, in which an unbroken arch is
the rule; in the cat, as will be described in the following pages,
and in the pig, the same type of development is followed, but a perfect arch would seem not to be produced ordinarily. In the rabbit
the condition is still more rudimentary, and one must agree with
Lewis that evidence of a fifth aortic arch in this form is wanting,
Fro. 6.-Reconstruction of the aortic arches of a 5.6 mm. cat embryo.
Serles 110. Columbia University Collection. Ventral view. x 50.
while the observations on the sheep and the rat are still incomplete, as
giving evidence for a vessel of the type described above.
A condition very similar to that occurring in man and the mole.
but, in general, more rudimentary, was found by the writer in the
cat. I n embryo Series 11 (Fig. 5 ) on the right side a spur extends
dorsad from the aortic bulb, between the fourth and pulmonic arches
(arch 6). .This spur occupies the position from which a fifth arch
586
Calvin B. Coulter.
would develop and resembles in all respects the anlages from which
the other arches arise. The sixth arch is complete, and gives off a
short pulmonary artery on the right side. I n addition to the spur
of the fifth aortic arch, there is a short vessel connecting the dorsal
ends of the fourth and sixth arches, very similar to the anastomosis
between the two arches found in the rat by Tandler and to the vessel
between the fourth arch and the root of the pulmonic in the pig
described by Lehmann. On the left side there was to be found no
FIG.7.-Photomicrograph of n transverse section through the fourth, fifth
and sixth branchial arches of a 6.6 mm. cat embryo. Right side. Series 110.
Columbia University Collection.
trace of a fifth aortic arch. The fourth and fifth pharyngeal ponches
have not separated in this embryo and consequently the fifth branchial
arch is not clearly marked out.
I n an embryo of 5.6 mm. ,(Series 110, Fig. 6) the second aortic
arches have lost their connection with the dorsal aorta, and their
~ e n t r a lremnants are disintegrating. There is on the right side a
spur of the fifth arch from the aortic bulb similar to that shown in
the preceding embryo, and in addition, a spur from the dorsal root
of the pulmonic arch, r i t h a blind vessel between them, almost con-
Aortic Arches of the Cat.
587
tinuous with the ventral spur, and running parallel to the arches on
either side. Each pulmonic arch joins the dorsal aorta by three
distinct roots, not clearly shown in the figure. On the left side two
spurs project from the dorsal end of the pulmonic arch, the larger
of which is directed ventrad between the fourth and fifth branchial
pouches. The fourth or most caudal pharyngeal evagination has
grown out, in its dorsal portion, into two divisions, the fourth and
fifth branchial pouches, which are shown in section in Fig. 7, through
the right side, and Fig. 8, through the left side. The photomicrographs show also the distinct character of the fifth branchial arch,
and the two ectodermal grooves in the floor of the sinus precervicalis. The ventral portion of the fourth pharyngeal evagination
remains undivided and as a result the fifth branchial arch is very
short. This stage marks the highest development of the fifth aortic
and branchial arches in the cat; in later stages the development is
retrogressive.0
I n embryo Series 138, 7 mm. in length (Fig. 9), the first aortio
arches have entirely disappeared, and the second arches are mere
stubs which break up into capillaries, There is no fifth aortic arch,
but the fifth branchial arch is very clearly marked out by the ectodermal grooves on the outside, and as in Series 110 (Figs. ‘7 and 8)
lies to the outer side of the fourth and sixth branchial arches. The
dorsal end of the sixth aortic arch is very large, and on the right side
shows a peculiar grooving which is suggestive of a division into
two much longer roots than found elsewhere. I n this and the pre‘Since the completion of this paper, Tandler has published in the Anat.
Hefte, 115 Heft (38 Bd.. Heft 2 ) , a careful description of the aortic arches
and related pharyngeal pouches to be found in human embryos. His account
agrees remarkably with mine. In man, however, the fourth and flfth pouches
a r e derived from the ventral portion of the last pharyngeal evagination, and
become more widely separated and distinct structures than in the cat. Correspondingly, the fifth aortic arch attains a more complete development. The
pouches of the cat have been made the subject of a careful study by Henry
Fox, whose article on “The Pharyngeal Pouches of the Mammnlia” has appeared since the completion of the present work in the Am. Jour. of Anat.,
Vol. VIII, No. 3. Hie results are entirely in accord with mine, although he
makes no mention of a fifth pouch, which I interpret as a division of his
“dorsal process of tho fourth pouch.” An indication of this separation into
two pouches is to be Been on the left side in his Fig. 60.
Calvin €3. Coulter.
588
Fro. S.-Sarne
FIG.g.-Reconstructlon
as Fig. 7. Left side.
of the aortic arches of a 7 mm. cat embryo. Seriea
138, Columbia University Collection. Right aide.
x
50.
Aortic Arches of the Cat.
589
ceding embryo the fourth and fifth branchial pouches are distinguishable, but their lumina are becoming obliterated, and their
common connection with the pharynx cavity is being elongated and
constricted off. Traces of the fourth pouch are to be found in
embryos of 8 and 9 mm., but in later stages it apparently disappears completely. .
Fro. 10.-Reconstruction of the aortic arches of a 9 mm. cat embryo. Series
19, Princeton University Collection. Right side. x 30.
In an embryo of 6 mm. (Series 129, not figured) the dorsal root
of the sixth aortic arch is very large, as in the Series 110 (Fig. S),
and a similar but longer spur arises from the base of the left pulmonk arch and ends blindly in the substance of the fifth branchial
arch.
Whatever the significance of the arterial spurs in the cat may
be, it is certain that we have here, outlined by the five entodermal
pouches on the inside and the corresponding ectodermal grooves on
590
Calvin B. Coulter.
the outside, six branchial arches. The fifth is a diminutive structure
and occupies a p i t i o n relatively dorsal and lateral to the other
branchial arches. The facts observed point to the conclusion that
ordinarily no B t h aortic arch is completely developed in the cat;
and it seems more than probable that the incomplete development and
FIG.11.-Reconstruction of the aortic arches of a 10 mm. cat embryo. Series
101, Columbla University Collection. Right side. X 28.
uncertain character of the fifth aortic arch is merely an expressiun
of the incomplete development of the fifth branchial arch. It may
well be that the anastomoses and irregular roots about the base of
the pulmonic arch which have been so generally described in the
mammalia are evidence of an assimilation of the fifth aortic arch
into the pulmonic, beginning at their dorsal extremities.
Aortic Arches of the Cat.
591
The ventral anlage of the sixth aortic arch appears first, as a
bud from the ventral end of the fourth arch (Fig. 4). Somewhat
later a dorsal bud grows out from the mesial side of the dorsal aorta,
and the completed arch pursues a curved or bent course around the
fourth an1 H t h pouches. The dorsal root of the pulmonic arch in
every case, from its first appearance until after the buds of the
pulmonary arteries arise, was found to be pierced by two or more
“islands.” The significance of this has been referred to above. .4t
FIQ. 12.-Reconstruction of the aortic arches of an 11.6 mm. cat embryo.
Series 29, Princeton University Collection. Right sida x 27.
about the time that the rudiments of the fifth aortic arch appear,
(Figs. 5 and 6) the pulmonary arteries begin to develop from the
middle of the sixth or pulmonic arches. Their development is very
similar to that described by Bremer’O (1901) in the rabbit. They
grow caudad, following the curve of the dorsal aorta, on each side
of the trachea. The aortic bulb now begins to lengthen out between
the fourth and sixth arches, and to divide into the short systemic
UBremer, J. L. On the Origin of the Pulmonary Arteriea in Mammala
Am. Jonr. Anat., Vol. I.
592
Calvin .B. Coulter.
and pulmonic trunks (Figs. 9, 10 and 11). In this process, the
pulmonic trunk is twisted from right to left, and so comes to lie on
the left side of the systemic trunk. At the same time the ventral
ends of the two pulmonic arches are brought into contact, and they
fuse together up to the point where the pulmonary arteries are given
off (Figs. 11 and 12).
The later history of the aortic arch system is too well known to
require any comment, and I leave the description at this point.
Received for publication July 9, 1909.
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