THE MYOLOGY OF AMIURUS CATUS. 315 



should be able to point to homologous muscles in the lower forms. 

 Can this be clone '? As to the Ganoids, to which one would naturally 

 turn, I 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. 1 In the Elasmobranchs 2 

 however, there are muscles with a certain amount of similarity. In 

 Chimcer i 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 R. maxillaris inferior trigemini. 

 The Plagiostomi present a muscle even more analogous. It is absent 

 in Heptanchus, in Acanthias, but strong in Scyllium, 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 trigeminus, which runs 

 over the muscle into the integument of the upper lip. Vetter terms 

 this muscle the lev. 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. arc&s palatini to act as an abductor 

 tentaculi also accords with it. 



3. Musculus Intermandibularis, (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— Lo>:. cit. 



2 Vetter— Untersoh. ziir vergl. Anat der Kiemen-und Kiefer-Muskeln der Fische. Th. I., 

 Jen. Zeit. Bd. viii. 



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