Nong) J7USCLES AND NERVES IN AMIA CAEVA. 585 
mandibularis, which it overlaps slightly ventrally, and is inserted 
in a fascia or aponeurosis which seems to extend across the 
ventral as well as the dorsal surface of that muscle. 
The facial nerves in both Galeus and Carcharinus come to the 
outer surface of the head along the front edge of Csd2. Sev- 
eral branches are sent backward to that muscle as the nerve 
reaches the outer surface, or even before it reaches the surface. 
A large branch, corresponding apparently to the ramus mandib- 
ularis facialis in Amia, is then sent downward in front of the 
main truncus. After giving off this important mandibular 
branch, the remaining, larger part of the facial nerve continues 
downward and backward, immediately behind the upper or hind 
edge of the upper jaw, to the point where the hindmost bundle 
of the anterior part of the ventral constrictor is attached to the 
hind edge of the mandible. There a branch, apparently sensory, 
is sent medianward and forward across that bundle. After 
giving off this branch, and after having sent several branches 
to the posterior portion of the constrictor, the remainder of the 
facial nerve passes internal to the hindermost bundle of the 
anterior portion of the muscle, and, lying along the outer sur- 
face of the inner, deeper layer of the muscle near its lateral 
edge, runs medianward and forward, sending branches to the 
deeper muscle and also to the superficial one. A large and 
important branch, if not the main nerve itself, enters the super- 
ficial muscle near the front edge of the inner, deeper one, and 
not far from the point where the superficial muscle is entered 
by the branch already described of the r. maxillaris inferior 
trigemini. This part of the facial nerve is unquestionably the 
r. hyoideus of Amia, and the inner, deeper muscle, along the 
outer surface of which it lies, the only part of the ventral con- 
strictor of the hyoid and mandibular arches that has become 
an even fairly independent muscle, is the hyohyoideus either 
wholly or in part. 
This muscle, the hyohyoideus, is apparently much more differ- 
entiated in Galeus and Carcharinus than in either of the three 
selachians described by Vetter, for in them the muscle is said 
to arise from the inner surface of a tendinous streak or aponeu- 
rosis that forms the median, ventral portion of the superficial 
