On the origin of the hyomandibula of the teleostomi

Abstract

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 reducidos.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 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 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 257