On the Origin of the Hyomandibula of the Teleostomi

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 dorso- antero-mesialmente en cada arc0 formando un itngulo con- siderable 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 articu- lares anterior y posterior de la hiomandibula, y en el arc0 mandibular a 10s procesos ascendente. y 6tico del palatocua- drado. El simpl6ctico es, probablemente, una parte de la barra branquio-radial anterior del arc0 hial y el interhial 10s elemen- tos epales y faringeos del arco, fusionados y relativamente muy reducidos. Translatlon by Dr. JoSe Nonidez, Columbia University AUTHOR’B AB8TRACT OF THIS PAPER E5UED BY TEE BIBLIOQRAPEIC SERVICE ON THE ORIGIN OF THE HYOMANDIBULA OF THE TELEOSTOMI EDWARD PHELPS ALLIS, JR. Menton, France ONE FIGURE 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 chondrifi- cation 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 to the hyal arch were said to 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 interar- cula 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 257 258 EDW.ARD PHELPS ALLIS, JR. 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 rep- resented 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 re- spective 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 to 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 cov- ered 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 to 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 HYOMANDIBULA OF THE TELEOSTOMI 259 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 ex- amined 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 supra- and 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 trun- cus 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 Wij he 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 Polyp- terus 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 260 EDWARD PHELPS ALLIS, JR. 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 Wij he 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 dor- sally 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 to form a practi- cally 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 mus- cles have pulled the distal (ventral) end of the epibranchial up- ward, and that element and the pharyngobranchial are then directed ventro-antero-niesially at 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- HYOMANDIBULA OF THE TELEOSTOMI 261 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.

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