378 
EDWARD PHELPS ALLIS. 
intermandibularis. Whether or not this intermandibularis, 
innervated by the nervns facialis, was overlapped externally 
by an intermandibularis derived from the corresponding- 
portion of the mandibular myotome, and innervated by the 
nervus trigeminus, cannot be told from dissections of the 
adult, but it is certain that, in the adults of living fishes, these 
two muscles are indistinguishably continuous one with the 
other. There is, accordingly, question as to where one 
muscle ends and the other begins, and it is frequently asserted 
that that part of the muscle that is of mandibular origin has 
lost its primary innervation by the nervus trigeminus and 
secondarily acquired innervation by the nervus facialis. It 
is accordingly important to know the relations of the nervus 
facialis to these muscles. 
The ramus hyoideus facialis, as shown in nearly all of 
Vetter’s (1874), Ruge’s (1897), and Luther’s (1909) figures of 
the Selachii, leaves the external surface of the hyal con- 
strictor to acquire a position between the musculi interhyoideus 
and interinandibularis and does not reappear on the external 
surface of the latter muscle. This is not, however, invariably 
the case, for in one of Luther’s figures of Heptanchus (1. c. 
p. 75) so-called motor branches of the^ nerve are shown 
reappearing on the external surface of the intermandibularis 
near its anterior end, and in the same author’s figures of 
Chlamydoselachus, Heterodontus, Squalus, and Etmopterus, 
small branches of the nerve are also shown reappearing on 
the external surface of the muscle, but it is not said that they 
are motor nerves, as in the case of Heptanchus. In Chlamy- 
doselachus one of these small branches is shown re-entering 
the muscle. Ruge found no branch of the nervus trigeminus 
going to any part of the musculus intermandibularis in any 
of the fishes examined by him. Luther, on the contrary, 
found branches of that nerve going to, and apparently 
innervating, the anterior part of the intermandibularis in all of 
the Plagiostomi examined by him excepting only Chlamydo- 
selachus and the Notidanidas. In his earlier work (1909) 
he concluded, in accord with Fiirbringer (1903) and 
