674 - PaaS. [Vor. XII. 
portion arises from the anterior and ventral surfaces of the 
small anterior and ventral articular process of the hypo- 
branchial, and between its fibres, on this same process, is 
inserted one of the two dorsal ends of the ligament from which 
one of the two arms of the branchiomandibularis arises. The 
other dorsal end of the ligament is inserted on the second 
hypobranchial and on the interarcual ligament connecting that 
hypobranchial with that of the third arch. 
The obliquus ventralis of the fourth arch is found as three 
distinct and separate muscles. One of them (Ov./V") corre- 
sponds to the outer or proximal portion of the muscles of the 
other arches. It arises from the anterior half of the ventral 
surface of the fourth hypobranchial and from the base of the 
small articular process of that piece, and is inserted on the 
anterior end of the ceratobranchial of the arch. The second 
muscle (Ov./V*) corresponds to the distal portion of the mus- 
cles of the other arches. It is a large, spindle-shaped muscle, 
the largest of all the obliqui, arises from the hind surface of 
the small articular process of the third hypobranchial, and, run- 
ning almost directly backward ventral to the proximal portion 
of the muscle and ventral to the anterior transversus ventralis, 
is inserted by a long and slender tendon on the ceratobranchial 
of the fifth arch near its anterior end and along the anterior 
side of the pharyngo-clavicularis externus. It may arise in part 
from or be attached to the fourth hypobranchial where it passes 
across it. The third muscle (Ov./V2) lies immediately dorsal 
to the anterior end of the second muscle and is undoubtedly a 
derivative of that muscle, for in 19 mm. specimens the two are 
found as a single muscle with no trace whatever of separation. 
It extends from the posterior surface of the small articular 
process of the third arch to the anterior surface of the corre- 
sponding process of the fourth arch. As all three muscles are 
innervated by branches of the nerve of the fourth arch, the 
large ventral one cannot be properly considered as the obliquus 
of the fifth arch, as McMurrich from its insertion concluded 
(No. 76, p. 133). 

