V ISCERAE ARCHES OF THE GNATHOSTOME FISHES. 383 
laris were of mandibular origin, for the muscle would then 
have lain primarily anterior and hence external to the nervus 
facialis, and it is difficult to conceive how certain portions of 
it, still retaining* their primary insertion on the mandibula, 
could have shifted from this primarily anterior and external 
relation to the nerve to a posterior and hence internal isola- 
tion to it. And as the muscle in no way lies in the path of, 
or interferes with the nervus facialis, it is difficult to conceive 
a reason for the perforation of the muscle by the nerve. 
The interhyoideus and intermandibularis muscles of 
Chlamydoselachus could accordingly both be of facialis 
origin, so far as the relations of nerve and muscle are con- 
•cerned, but in all probability only that portion of the inter- 
mandibularis that lies anterior to the point where the nervus 
facialis definitely disappears from its external surface could 
be of mandibular origin. And if this portion of the muscle 
be of mandibular origin, as several authors have maintained, 
I consider it certain that it is innervated by a branch of the 
nervus mandibularis trigemini, and that that branch has 
simply been missed in dissections, my own included. That it 
is possible that this nerve has been so missed is shown by the 
fact that in Heptanchus, where Furbringer and Luther both 
found the intermandibularis innervated by the nervus facialis 
alone, my assistant, Mr. John Henry, finds, on both sides of 
the head of one of three specimens of this fish that were 
•examined, a branch of the nervus mandibularis trigemini 
going to the intermandibularis in a position strictly com- 
parable to that shown by Luther in several of the Selachii 
examined by him, while in the other two specimens it was not 
found. 
Edgeworth says that the musculi interhyoideus and inter- 
mandibularis, apparently wherever found in the vertebrate 
series, are not developed from the myotomes of their respec- 
tive arches, but from related portions of the wall of the 
coelomic cavity, and that they accordingly have no homologues 
in the branchial arches. According to him (loc. cit., p. 178) ; 
•“ The cephalic coelom disappears in the mandibular and hyoid 
