The homologies of the hyomandibula of the gnathostome fishes

This is the authors' abstract. We don't add key points for this paper.

Work that I have under way on the cranial anatomy of Chlamydoselachus has led to certain conclusions regarding the hyomandubula which, if correct, are of considerable morphological importance.They are based on the assumption, which seems practically established by my work, that the dorsal ends of all of the so-called inner cartilaginous bars of all of the visceral arches, in all of the gnathostome fishes, always lie ventral to the vena jugularis, and that when parts of the cartilaginous bars of the adult fish articulate or fuse with the neurocranium dorsal to that vein, those parts are derived either from the external cartilaginous bars of the arches, or from interarcual cartilages developed in, or in relation to, the dorsal interarcual ligaments.The terms inner and external cartilaginous bars, or arches, are here used with the significance commonly given to them, but my work tends decidedly to confirm Dohrn's conclusion that the so-called inner cartilaginous bars of the branchial arches of the gnathostome fishes, and not the external ones, are the homologues of the cartilaginous branchial arches of the Cyclostomata.The cartilages which form the so-called external arches of the gnathostome fishes are commonly called the extrabranchials in whatever arch they may be found.Parker ('76) limited the use of this term to the external cartilages of the gill-bearing, branchial and hyal arches, employing the term extraviscerals to designate, collectively, these cartilages and certain others, the so-called labial cartilages of his descriptions, which he considered to be their serial homologues in the prehyal arches.