•376 
EDWARD PHELPS ALLIS. 
muscles would naturally retain tliei r primitive relations to 
the vena jugularis, and when they acquired, by their dorsal 
ends, insertion on the neurocranium, that insertion would be 
dorsal to the vein; and such I find to be the relations of the 
muscles to the vein in Amia, Lepidosteus, Polypterus, 
Polyodon, and several Teleostei that I have examined for 
this special purpose, with the single exception of Ameiurus. 
In Ameiurus the vein passes over the posterior edge of the 
adductor hyomandibularis, and then lies dorsal (external) to 
that muscle, Ameiurus thus being exceptional in this as also 
in several other cranial features (Allis, 1915, p. 566). 
Vetter (1878, pp. 532-534), also, considered that these 
muscles of the Teleostei were derived from what corresponds 
to the dorsal portion of the constrictor superficialis of the 
hyal arch of the Selachii, but he said it was difficult to con- 
ceive the intermediate stages in such an extraordinary change 
of position. The development of the hyomandibula in the 
manner that I have suggested wholly removes this difficulty. 
The levatores arcuum branchialium were considered by 
Vetter to represent remnants of the musculi interbranchiales 
of the Selachii, this conclusion being evidently based on the 
assumption that the constrictores superficiales of the Selachii 
had entirely disappeared in the Teleostei, as he had pre- 
viously concluded that they had disappeared in Chimasra and 
Acipenser. • 
In an earlier work I said (Allis, 1897, p. 751) that : “ The 
adductor hyomandibularis is probably developed from a 
muscle comparable to one or more of the interarcual muscles 
of the branchial arches of selachians, and is thus homodyn- 
amous with the levators of the branchial arches of teleostomes, 
and not with the adductor inandibulae. The adductor operculi 
and levator operculi, at least the latter, are derived from the 
interbrancbial muscles of their arch, and are thus homodyn- 
amous with the levator arcus palatini, and not with the 
levator muscles of the branchial arches. ” These conclusions 
were based on my interpretation of Vetter’s descriptions of 
the Selachii, and on the acceptance of his conclusion that the 
