No.3.) WUSCLES AND NERVES IN AMIA CALVA. 569 
The muscle Addy, in Scymnus and Acanthias (No. 124, p. 
448), arises partly tendinous from the under surface of the skin, 
immediately behind the eye, and immediately in front of the 
postorbital process. It runs downward and backward, and is 
inserted on the outer surface of the adductor mandibulae, being 
there more muscular than in its upper portion, and being in part 
a direct continuation of the fibres of Csv2, which Vetter con- 
siders as the ventral half of the superficial layer of the con- 
strictor of the hyoid arch. In Heptanchus Addy seems, from 
Vetter’s figure, to arise from the lower rather than the upper 
corner of the orbit, as in Scymnus; it runs more nearly back- 
ward, its hindermost fibres are inserted on the cartilage at the 
hind corner of the upper jaw, and it has no connection with the 
muscle fibres of the ventral half of the constrictor. The inner- 
vation of the muscle is not given in either fish described. In 
Mustelus and the rays, Tiesing does not describe this muscle. 
That it is not peculiar to the fishes described by Vetter is 
shown by Carcharinus, where a muscle is found closely resem- 
bling that of Heptanchus. It arises near the upper corner 
of the eye, is inserted in part on the lower end of the hyoman- 
dibular, and its posterior portion is crossed by many branches 
of the facial, which go entirely or in large part to cutaneous or 
subcutaneous tissues. The muscle is apparently innervated by 
branches of a nerve which arises inside the cranial cavity, from 
the main truncus or ganglion of the trigeminus, the nerve issuing 
immediately behind the eye, around the front edge of the levator 
maxillae superioris, and then turning backward along the outer 
surface of Addy. 
Addy is considered by Vetter as the last remnant of the super- 
ficial constrictor of some one or more preoral arches (No. 124, 
p. 448). Its position, however, in Scymnus and Acanthias, its 
connection with the adductor, and its continuity with the 
ventral half of the constrictor, seem to indicate that it belongs 
to the mandibular arch, and that it is derived from the dorsal 
half of the superficial constrictor of that arch. Its innervation, 
if the innervation found in Carcharinus be correct, agrees 
closely with that of the levator arcus palatini in Amia, and such 
slight changes only would be needed in its origin and insertion, 
