No. 3.] MUSCLES AND NERVES IN AMIA CALVA. 639 
along the inner surface of the mandible, could be easily derived 
from that in selachians as given by Vetter. In Heptanchus 
what seems to be the nerve is shown lying along the posterior 
edge of the mandible ; from this position, as the hyoideo-man- 
dibular fold of Amia was formed, the nerve could as naturally 
come to lie along the inner surface of the mandible as along 
the lateral surface of the hyoid. The more superficial nerves 
r.ghs and r.ghi of Amia would at the same time acquire their 
somewhat peculiar course. 
The nerves ~ghs and 7.ghi vary greatly in importance and 
in position in different fishes. In Gadus they, and part also of 
branch 4 of the maxillaris inferior of Amia, seem to be repre- 
sented by a single nerve, the larger portion of which lies along 
the lower edge of the mandible, small branches only passing 
into or toward the hyoideo-mandibular fold. In siluroids they 
are in all probability the nerves of the submandibular and 
mental tentacles, the nerves called by Pollard the ramus sub- 
mandibularis and ramus mentalis trigemini. Pollard states 
(No. 97, p. 411) that these nerves in siluroids either contain, 
or are accompanied by, motor fibres, destined to supply the 
muscles that move the tentacles. The muscles themselves 
he does not describe. As all tentacle muscles in siluroids are 
said to belong (No. 97, p. 382) to a special system, not homolo- 
gous with the metameric body muscles, they must either have 
entirely disappeared in Amia or have become absorbed in other 
muscles. 
In Auchenapsis and Callichthys Pollard describes a ramus 
mandibularis externus trigemini, which he says (No. 97, p. 410) 
may be a dissociated branch of his ramus mentalis trigemini. 
The mentalis lies internal to the coronoid process of Meckel’s 
cartilage, the externus external to that cartilage and external 
to the mentalis (No. 97, p. 391). In Callicthys the externus 
supplies the anterior face of the mental tentacle. Whether 
this nerve finds its homologue in one of the branches of branch 
4 of the maxillaris inferior trigemini of Amia, in some part of 
nerves 7.ghs and r.ghi, or in a branch of the facialis, seems 
open to question. It is to be noted that in Callicthys there is 
no lateral line canal in the mandible (No. 94, p. 534), and that 
