THE MYOLOGY OF AMIURUS CATUS. BLO 
should be able to point to homologous muscles in the lower forms. 
Can this be done? As to the Ganoids, to which one would naturally 
turn, [ have not been able to consult any account of their muscula~ 
ture, with the exception of Vetter’s description of Acipenser, in 
which, apparently, no homologue is present.!- In the Elasmobranchs? 
however, there are muscles with a certain amount of similarity. In 
Chimer the lev. anguli oris consists of two portions, of which the 
posterior arises principally from the lower border of the orbit, is in- 
serted into the inner surface of the posterior inferior labial cartilage, 
and is innervated by twigs from the 2. maxillaris inferior trigemini. 
The Plagiostomi present a muscle even more analogous. It is absent 
in Heptanchus, in Acanthias, but strong in Scylliwm, and arises from 
the under surface of the orbital regions of the skull. It passes for- 
wards and is united by connective tissue to the posterior superior 
labial cartilage, union occurring also with the add. mand. It is inner 
vated by a twig of the second branch of the ¢rageminus, which runs 
over the muscle into the integument of the upper lip. Vetter terms 
this muscle the /ev. labii superioris. 
The difference between this muscle and the add. tent. may possibly 
be explained by the presence of the membrane bones in the Teleos- 
tean skull, but nevertheless it seems that the first hypothesis is to be 
preferred. As I have already shown in a preceding paper, the Sil- 
uroids must have branched off very early from the original stem of 
the Teleosts, and have undergone much specialization. The presence 
of the tentacle itself is a great specialization, and since it would be of 
advantage to the fish that this should be capable of voluntary move- 
ment, there would be a tendency for a separation of certain fibres of 
the add. mand. for this purpose, which tendency would in the course 
of time result in the production of a perfectly distinct muscle. The 
innervation points very strongly to this theory, and the adaptation 
of the anterior fibres of the add. arcés palatina to act as an abductor 
tentaculi also accords with it. 
3. Muscutus IntermMaAnpiBuLaris, (No. 21, Cuv.) (Fig. 3, Im.) 
This muscle is seen on removing the integument from the under 
surface of the head. It lies immediately behind the symphysis of 
the mandible, running transversely from one ramus to the other. 
1 Vetter—Loc. cit. 
2 Vetter—Untersch. ziir vergl. Anat der Kiemen-und Kiefer-Muskeln der Fische. Th. L., 
Jen. Zeit. Bd. viii. 
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