THE MYOLOGY OF POLYODON 129 
V. HYPOGLOSSAL MUSCLES 
That portion of the ventral body musculature which lies ante- 
rior to the shoulder girdle is in intimate relation with the man- 
dibular, hyoid and branchial arches. In fishes generally this 
musculature is supplied by the first spinal nerve in anastomosis 
with one or more postvagal roots (the ‘hypoglossal nerve’), or 
by the first and second spinal nerves. Postvagal roots probably 
occur in all the ganoids. In Amia there are two. Van Wijhe 
(l.c.) states that he was unable to detect any in Polyodon, but 
the present writer finds a very delicate strand which leaves the 
medulla close to the root of the vagus and emerges from the 
skull through a minute occipital foramen. It ultimately joins 
with the first spinal nerve, i.e., the first postvagal nerve which has 
both ventral and dorsal roots. The conjoined nerve supplies, so 
far as could be determined, the whole hypoglossal musculature. 
This musculature in Selachians consists of the coraco-arcuales 
(Vetter) which in the simpler forms, such as Heptanchus, extends 
forward from the coracoid, giving off slips to each branchial 
arch, to the hyoid and to the mandible. In the higher forms 
these elements are variously modified and reduced. The ques- 
tion of the relation to the trunk musculature cannot be fully 
considered in this connection. For a full discussion of this mus- 
culature in lower forms, the reader is Teles especially to the 
work of H. V. Neal (’97). 
The elements of the original coraco-arcuales that remain in 
Polyodon are the following: 
M. branchiomandibularis: figure 3, m.bmd. 
The branchiomandibular muscle is bilateral at its origin and 
insertion, but single and medial throughout most of its length. 
Its fibers arise on either side directly from the hypobranchial 
cartilage of the third arch just medial and anterior to the inser- 
tion of the tendon of the coraco-arcualis (hyopectoralis) to that 
arch. The muscle slip on either side passes forward, downward, 
and inward, medial to the main tendon of the coraco-arcualis, 
to meet its fellow of the opposite side at a point ventral to the 
JOURNAL OF MORPHOLOGY, VOL. 24, No. 1 
