578 ALLIS. [VoL. XII. 
thus finds no homologue in Petromyzon, Bdellostoma, or other 
fishes, and it seems safe to assume that that part of it that lies 
under the opticus corresponds to the ramus ad musc. levator 
maxillae superioris and parts of the ramus maxillaris superior 
trigemini combined of Amia, while the branch above the opti- 
cus is the true ramus ophthalmicus. Whether these deduc- 
tions be correct or not, I certainly should not accept existing 
descriptions of these nerves as supporting Pollard’s dictum, 
based in part upon them, that “the topographical position and 
course of nerves is not of great importance”’ (No. 97, p. 397). 
c. Adductor Mandibulae. 
The adductor mandibulae proper in Heptanchus, Acanthias, 
and Scymnus, as described by Vetter, is an extremely simple 
muscle ; practically an uninterrupted and undivided layer of 
muscle fibres extending from near the upper edge of the pala- 
tine arch to the lower edge of the mandible. In Carcharinus 
and Galeus it is not so simple. In both these fishes the r. max- 
illaris inferior trigemini penetrates the muscle between a super- 
ficial and a deeper portion, which are entirely separate at and 
near the surface. A surface line extending upward and forward 
across the muscle, from, or from near, the corner of the mouth, 
marks the front edge of the superficial portion. The fibres of 
this superficial portion are inserted into a transverse tendinous 
formation, or aponeurosis, which extends inward and upward into 
the muscle from a curved surface line which extends from the 
corner of the mouth backward, outward, and upward toward the 
hind corner of the upper jaw. This tendon does not extend 
entirely through the muscle. It is inserted behind and above 
on the hind corner of the upper jaw, and in front it is attached 
to the dermis at the corner of the mouth. It is pierced by the 
r. maxillaris inferior trigemini, in Carcharinus at a considerable 
depth below the outer surface, in Galeus near that surface, the 
nerve in the latter fish coming outward toward the surface along 
the front edge and outer surface of the tendon. In Carcharinus 
the nerve, having pierced the tendon, or having even passed 
entirely beneath it near its front edge, continues for some dis- 
