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On the origin of the hyomandibula of the teleostomi.

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Resumido por el autor, Edward Phelps Allis, Jr.
Sobre el origen de la hiomandibula de 10s Teleostomos.
En Polypterus y otros Ganoideos las dos filas de branquias de
cada uno de 10s arcos branquiales anteriores estitn reforzadas
por radios branquiales cartilaginosos, y en Polypterus, las bases
de dichos radios se han fusionado para fonnar una barra branquio-radial. Estas barras branquio-radiales se proyectan dorsoantero-mesialmente en cada arc0 formando un itngulo considerable con el epibranquial y faringobranquial del mismo
arc0 y estitn dirigidas hacia puntos situados dorsalmente a la
vena yugular. En 10s Selacios, una de estas barras ha dado lugar
a 10s extrabranquiales de cada arco. En 10s Teleostomos barras
semejantes han dado lugar, en el arc0 hial, a las cabezas articulares anterior y posterior de la hiomandibula, y en el arc0
mandibular a 10s procesos ascendente. y 6tico del palatocuadrado. El simpl6ctico es, probablemente, una parte de la barra
branquio-radial anterior del arc0 hial y el interhial 10s elementos epales y faringeos del arco, fusionados y relativamente muy
Translatlon by Dr. JoSe Nonidez,
Columbia University
Menton, France
In a work published in 1914, I came to the conclusion that
there must be, in fishes, “a primarily somewhat independent
mass of mesoderm cells lying lateral to the neurocranium and
dorsal to the dorsal ends, of the mandibular and premandibular
arches, in the position of the pharyngeal elements of the branchial
arches, which pharyngeal elements are wanting, as independent
structures, in the mandibular and premandibular arches of all
fishes.” These cells were assumed to be capable of chondrification and to have given rise both to the ascending and otic
processes of the palatoquadrate of the Dipneusti, Amphibia and
Reptilia, and to the lateral wall of the trigemino-facialis chamber
of fishes and mammals. Similar cells related t o the hyal arch
were said t o have possibly given rise to some portion of the otic
capsule, and its derivative the operculum, and probably also to
the toleostean hyomandibula.
In a later work, published in 1915, I came to the conclusion
that the cartilages derived from the mesoderm cells above referred to had, in 311 probability, their serial homologues in the
extrabranchials and interarcual cartilages of the branchial arches
of the Selachii, the posterior articular head of the teleostean
hyomandibula being derived from the dorsal extrabranchial of
the hyal arch and the anterior articular head from the interarcula cartilage between that arch and the mandibular arch.
The symplectic was said to probably be a primarily independent
cartilage, and probably an hypertrophied middle one or ones of
the branchial rays of the mandibular arch. The single articular
head of the hyomandibula of the Chondrostei was said to apparently correspond to the anterior articular head of the teleostean
hyomandibula. The hyomandibula of Polypterus was left
largely out of consideration, but it was said that the suprapharyngobranchials of' van Wijhe's ('82) descriptions of that
fish and certain others of the Ganoidei were quite certainly represented in the extrabranchials of the Selachii, the suprapharyngobranchials accordingly being serial homologues of the posterior
articular head of the hyomandibula.
Since the publication of the work last above referred to, I
have had occasion to examine the branchial arches in Polypterus,
and I not only find that the suprapharyngobranchials of van
Wijhe's descriptions are simply the epibranchiale of their respective arches, but that there are, in each arch, cartilages that
quite certainly represent the special mesoderm cells that were
assumed, in the two works above referred to, to have given rise,
in the hyal arch, to the hyomandibula, and in the mandibular
arch to the ascending and otic processes of the palatoquadrate.
Van Wijhe, in the work above referred to, described, in the
dorsal half of the first branchial arch of Polypterus, a small cartilage that he considered to represent the epibranchial of the
arch, and two bones that he called the supra- and infrapharyngobranchials, the infrapharyngobranchial apparently being considered by him t o correspond to the typical selachian pharyngobranchial, and the suprapharyngobranchial to be a fifth element
of a complete and typical branchial arch. The epibranchial is said
to be almost completely concealed in a ligament that envelops
both it and the infrapharyngobranchial, and that has its insertion
on what Van Wijhe considered to be a part of the prootic covered by the thin lateral edge of the parasphenoid. The suprapharyngobranchial is said to be relatively large, to abut against
a cartilaginous portion of the lateral wall of the neurocranium,
and t o have its distal portion deeply grooved to lodge the efferent artery of the arch. In the second and third branchial arches
there is said to be no epibranchial, and it is said that the upper
ends of the supra- and infrapharyngobranchials of those arches
may be fused to form a short tube which encloses the efferent
artery of the arch. In the corresponding part of the fourth arch
there is said to be a small pharyngobranchial, but in the figure
given it is index-lettered as an infrapharyngobranchial.
In a 75-mm. specimen of Polypterus senegalus that I have examined in serial transverse sections, there is no trace of the independent so-called epibranchial cartilage described by van Wijhe
in the first branchial arch, and I also find no trace of it in adult
specimens of Polypterus bichir and Polypterus ornatipinnis.
In the first branchial arch of the 75-mm. specimen, the supraand infrapharyngobranchials of van Wijhe’s descriptions are
found as independent cartilages, and they are certainly simply,
respectively, the normal epibranchial and pharyngobranchial of
the arch. The epibranchial articulates by its distal end with
the ceratobranchial of its arch, and by the anterior corner of its
proximal end with the pharyngobranchial, and the posterior corner of its proximal end has been prolonged to form a stout process
which has acquired articular relations with the lateral wall of the
bulla acustica,there lying ventral to thevena jugularis and the truncus facialis. The pharyngobranchial articulates with the epibranchial, as above described, and, running anteromesially and somewhat ventrally, enters the angle between the lateral and ventral
(horizontal) plates of the ascending process of the parasphenoid,
and there has its attachment. In its course it lies imbedded in
the lateral surface of the thymus, dorsal to a stout ligament that
extends from the angle of the ascending process of the parasphenoid to the dorsal end of the ceratobranchial of the first
branchial arch, this ligament being the one that is said by van
Wijhe to envelop his epibranchial and infrapharyngobranchial.
A groove on the external surface of the epibranchial (suprapharyngobranchial of van Wijhe), between it and the pharyngobranchial (infrapharyngobranchial of van Wijhe) , lodges the
efferent artery of the arch.
In the adult specimens of both Polypterus bichir and Polypterus ornatipinnis, I find strictly similar conditions; but the epibranchial and pharyngobranchial have apparently fused with
each other, and each has undergone extensive ossification, the
two so-formed bones being in contact at their distal ends and
there immovably connected with each other. The process on the
posterior corner of the proximal end of the epibranchial has been
completely ossified, excepting the articular cap by which it
articulates with the lateral wall of the bulla acustica, and this
process of the bone is strictly similar to that shown by van Wijhe
in his figures of Amia and Lepidosteus, and by me in my figures
of Amia and Scomber (Allis, '97, '03). In Amia T did not find
the suprapharyngobranchial described by van Wijhe in that
fish, but in Scomber, in a, corresponding position, I found an
independent piece of cartilage that articulated with the pharyngobranchial of the second branchial arch and that I called a suprapharyngobranchial.
In the second and third branchial arches of all my specimens
of Polypterus, the 75-mm. one as well as the adults, the epibranchial and pharyngobranchial of each arch are completely
fused with each other, :and the anterior (lateral) and posterior
(mesial) edges of the so-formed piece have been produced dorsally so that they touch, or fuse with each other, dorsal to the
efferent artery of the arch, thus enclosing it in a short tube.
The nerve of the arch runs posteriorly dorsal to this tube, not
traversing it.
Each of the first three branchial arches of this fish is furnished
with two rows of branchiae, each row supported by cartilaginous
branchial rays the bases of which have fused t o form a practically continuous bar of cartilage, as shown in the accompanying
figure. The rays thus form a comb-shaped structure the base
of which is arched in a curve that corresponds approximately to
that of the branchial bar of the arch when the mouth is opened
and the branchial chamber expanded. When the mouth is
closed and the branchia'l chamber contracted, the levator muscles have pulled the distal (ventral) end of the epibranchial upward, and that element and the pharyngobranchial are then
directed ventro-antero-niesially a t a marked angle to the ceratobranchial. The comb-shaped structures formed by the branchial
rays of each arch can not undergo a corresponding change of
form, because of the relative rigidity of their basal bars, and the
dorsal portions of those bars, the parts related to the epibranch-
ial and pharyngobranchial of each arch, project dorso-anteromesially, but more mesially, and less anteriorly, than the dorsal
portions of the branchial bar, this leaving a wide space between
themselves and that portion of the branchial bar. The basal
bars of the rays, projecting dorsally, lie external t o the levator
muscles of the arch, and their dorsal ends, which lie dorsal t o
the vena jugularis, are there attached by connective tissues.
Fig. 1 Lateral view of the posterior portion of the neurocranium of Polypterus, showing t h e first branchial arch in place, with the related anterior series
of cartilaginous branchial rays, but the posterior branchial arches and the hyal
arch removed. X 2. br., branchial rays of first branchial arch; cbr., ceratobranchial; ehr., epibranchial; $r., facialis foramen; g . , groove for vena jugularis;
pbr ., pharyngobranchial ; ps., parasphenoid.
The nerve and efferent artery of the arch now pass ventral to
the anterior one of these two branchial-ray bars, and thenonward between the two bars onto the external surface of the
ceratobranchial of the arch.
In Amia, Lepidosteus and Polyodon cartilaginous branchial
rays similar to those of Polypterus are found, and their bases
are in contact with each other, but not so completely fused as in
Polypterus; and in these fishes, also, the branchial-ray bars project dorsal to the epibranchial and pharyngobranchial of the arch
to which they are related. There is accordingly every reason
to believe that similar conditions existed in the immediate ancestors of these fishes, and that in those fishes branchial rays,
capable of fusing with each other at their bases, were found also
in the hyal and mandibular arches. The dorsal ends of the
branchial-ray bars of the latter arches would then lie close t o
the bulging auditory portion of the neurocranium, dorsal to the
vena jugularis, and hence in a position to form, in the hyal arch,
a hyomandibula with one or two articular heads, and in the mandibular arch the ascending and otic processes of the palatoquadrate. The hyomandibula, thus formed, would lie in a plane
somewhat inclined to that of the branchial bar of its arch, and
the articulation of that bar with the hyomandibula would naturally be with its postero-internal surface, as is actually the case
in Polypterus.
The hyomandibula of Polypterus is always said to have but
a single articular head, and the nervus hyoideus facialis runs
outward posterior to that head, and the nervus mandibularis
facialis anterior to it. I however find, in my 75-mm. specimen
of this fish, a small and independent bit of cartilage lying immediately posterior to the cartilage that caps the actual articular
head of the hyomandibula, and the so-called accessory hyomandibula is developed in relation to it. On one side of one adult
specimen that was also examined, I find the dorsal edge of the
accessory hyomandibula capped with cartilage, that cap forming a posterior ext,ension of the cap on the articular head of the
hyomandibula ; and Traquair apparently shows similar conditions
in his figure of this fish ('70, fig. 6, pl. 6). On the other side of
the head of my specimen, this edge of the accessory hyomandibula
is covered with bone, this being as van Wijhe ('82) found it in
the specimen described and figured by him. A stout ligament
always extends from the head of the accessory hyomandibula to
the dorsal edge of the opercular process of the hyomandibula,
and lies posterior to the nervus hyoideus facialis; this ligament
and the accessory hyomandibula thus quite certainly representing the posterior articular head of the teleostean hyomandibula. The efferent artery of the arch lies postero-internal to
this ligament, thus corresponding, in its relations to the branchial
rays, to the posterior efferent artery of the Selachii. The position of the nervus mandibularis facialis, anterior to the anterior
articular head of the hyomandibula, is doubtless due to this
nerve having separated from the nervus hyoideus shortly after
the truncus facialis issued from its foramen, thus permitting it
t o slip over the dorsal end of the anterior branchial-ray bar before that bar had acquired articulation with the cranial wall.
The ventral end of the hyomandibula presents two angles, or
processes, one of which articulates with the interhyal and is
apparently formed by the posterior branchial-ray bar of the
arch, while the other articulates with the quadrate, forms the
so-called symplectic process of the hyomandibula, and is doubtless formed by the anterior branchial-ray bar. The interhyal
must then represent the coalesced and relatively geatly reduced
epal and pharyngeal elements of the arch.
In the Holostei and Teleostei the conditions are similar to
those in Polypterus excepting in that the posterior articular head
of the hyomandibula is more fully developed, and in that the
nervus mandibularis facialis does not separate from the nervus
hyoideus until after the truncus facialis has passed between the
two heads of the hyomandibula.
In the Chondrostei, the posterior articular head of the hyomandibula is wholly wanting, .this indicating that the posterior
branchial-ray bar has more or less completely aborted, and, doubtless in correlation with this, the interhyal has acquired articulation with the symplectic which must be either a detached portion
of the anterior branchial-ray bar or be derived, as suggested in
my earlier work, from branchial rays of the mandibular arch.
In the Plagiostomi, the hyomandibula articulates with the
cranial wall ventral to the vena jugularis, and is formed, in the
Selachii, by the epihyal, and in the Batoidei by the pharyngohyal
(Allis, '15). There is in these fishes but a single row of branchial rays, a posterior one, and it is found in the hyal as well as
in the branchial arches. Associated with these rays there are
so-called dorsal and ventral extrabranchials, which are currently
considered to be simply modified dorsal and ventral ones of the
branchial rays actually found in these fishes. Braus (’06), however, considers them to belong to an independent category of
skeletal elements, for, in embryos of Heptanchus, he found them
lying not only at a considerable distance from the branchial rays,
but also at right angles t o those rays and parallel to the inner
branchial bars. These relations t o the branchial rays at once
suggest a branchial-ray bar that has been developed either in
relation to those dorsal and ventral ones of the posterior row
that were primarily related to the pharyngeal and hyal elements
of the arch. If the extrabranchials have this latter origin, which
seeins probable, then the dorsal one would be of similar origin
to that here ascribed to the posterior articular head of the telecistean hyomandibula. The conclusions arrived at in my earlier
works, and briefly statred in the opening paragraphs of the present article, would then have to be modified simply by the substitution of the “anterior branchial-ray bar of the hyal arch” in
place of “an interarcual cartilage that lay between that arch
and the mandibular arch,” and the symplectic would be derived
from the anterior branchisl-ray bar instead of from the branchial
rays of the mandibular arch.
The conditJionshere found in recent Teleostomi and Plagioscami could evidently not be derived the one from the other without reversion to a type from which they both must have descended, and as there are no indications of any such reversion
having taken place, the separation of the two lines here indicated
must have taken place in very early geological times, for even
in the crossopterygian Tristichopterus, remains of which are
found in lower Devonian rocks, the hyomandibula must have
articulated with the neurocranium dorsal t o the vena jugularis,
for Traquair (’75) says that the posterior margin of the palatosuspensory apparatus, “apparently corresponding to the hyomandibular element,” gives articulation externally to the preopercular cheek-plate, and is itself connected dorsally with the
squamosal region of the cranium; each of which conditions indicatcs
that the hyomandibula lay external t o the vena jugularis and
articulated with the cranium dorsal to that vein.
Palois de CarnolBs, Menton, France
April 13. 1918
ALLIS, E. P., JE. 1897 The rranial muscles, and cranial and first spinal nerves
in Amia calva. Jour. Morph., vol. 12, Eoston.
1903 The skull, and the cranial and first spinal muscles and nerves
in Scoinber scomber. Jour. Morph., vol. 18, Lancs.
1914 ‘The pituitary fossa and trigemino-facialis chamber in Ceratodus
forsteri. Anat. Anz., Bd. 46, Jena.
1915 The homologies of the hyomandihula of the gnathostome fishes.
Jour. Morph., vol. 26. Philnda.
B R ~ U SH.
1906 Fher d r n cmhryonalen Kiemenapparat von Heptanehus.
h a t . .inz., Ed. 29. Jena.
R. H. 1870 On the cranial osteology of Polypterus. Journ. Anat.
and Physiol., vol. 5, London.
1875 Structure and affinities of Tristichopterus alatus. Trans. Royal
Soc., vol. 27, Edin.
WIJHE, J. W. VAR’ 1882 fiber das Visceralskelet und die Nerven des Kopfes der
Ganoiden und von Ceratodus. Niederl. Archiv fur Zool., Bd. 5, H. 3.
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