THE HOMOLOGIES OF THE HYOMANDIBULA OF THE 
GNATHOSTOME FISHES 
EDWARD PHELPS ALLIS, JR. 
Menton, France 
ONE FIGURE 
Work that I have under way on the cranial anatomy of Chla- 
mydoselachus has led to certain conclusions regarding the hyo- 
mandubula 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 
enathostome 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 la- 
bial cartilages of his descriptions, which he considered to be their 
serial homologues in the prehyal arches. The use of the term 
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JOURNAL OF MORPHOLOGY, VOL. 26, No. 4 
DECEMBER, 1915 
