THE MYOLOGY OF POLYODON 131 
cle, however, is directly continuous with the great ventral muscu- 
lature (fig. 9) of which it appears to be simply an anterior pro- 
longation. Several deep intermuscular septa, in serial continuity 
with those of the body musculature, cross the belly of this muscle 
obliquely. The muscles of the two sides meet in front of the 
pericardium and unite, but the two halves are separated by a 
median aponeurotic septum into which fibers are inserted. The 
median muscle now grows rapidly smaller anteriorly and passes 
through a longitudinal canal formed between the two infra- 
clavicles. In front of them the two halves again separate and 
are produced forward as long slender superficial tendons (fig. 3). 
The main continuation of each tendon is inserted on the hypohyal 
cartilage. Dorsal slips are also given off from the tendon to the 
first, second and third basibranchial cartilages. 
Innervation. The muscle is supplied by the combined first 
spinal and post-vagal nerve. Its branch arises from a large trunk 
near the origin of the pharyngoclaviculares and may even pass 
through them to reach its destination. Within the muscle it* 
can be traced a considerable distance and probably successful 
dissection would carry its terminal ramifications forward to the 
branchiomandibularis. 
Blood supply. The arteries which reach this muscle are: in 
front, the large posterior branch of the posterior commissure of 
the hypobranchial system; behind, the infra-pericardial branch 
of the coronary. : 
Action. It depresses the whole hyoid and branchial apparatus. 
This muscle agrees very well with the coraco-arcualis anterior 
of Acipenser, at least in so far as its insertion is concerned. In 
Acipenser there is also a coraco-arcualis posterior which is in- 
serted on the fourth hypobranchial cartilage. This is lacking 
in Polyodon. The above described (anterior) coraco-arcualis of 
Polyodon is especially interesting since here we find it actually 
continuous with the longitudinal body musculature, a condition 
which apparently does not often obtain in animals with a pec- 
toral arch. In this respect it recalls Petromyzon (Neal, ’97). 
