No. 3.] MUSCLES AND NERVES IN AMIA CALVA. 675 
b. Transversi Ventrales. 
The transversus ventralis anterior (Z7va) arises in a line along 
the middle of the ventral surface of the fourth hypobranchial 
on one side of the head, internal to and dorsal to the obliquus 
of the arch but ventral to the artery of the arch, and extends 
across the middle line, ventral to the second and third basi- 
branchials and dorsal to the sinus arteriosus, to the fourth 
hypobranchial of the other side. It is always composed of two 
or more more or less distinct muscles or muscle bundles; the 
muscle bundles, when they exist, —or when they do not the ven- 
tral fibres of the muscle, —always crossing each other at a con- 
siderable angle, the muscle fibres or muscle bundle of the right 
side always lying ventral to that of the left side. The dorsal 
muscle where the separation is complete, or the dorsal fibres of 
the muscle where it is incomplete, always run directly across 
the middle line of the head. The muscle is innervated in all 
its parts by the nerve of the fourth arch and the muscle in its 
posterior portion is often continuous with the obliquus of that 
arch. 
The transversus ventralis posterior (7zvp) is formed by two 
muscles, each of which belongs distinctly to its own side of the 
head and does not, as in the case of the anterior transversus, 
cross the middle line of the head to be inserted on the opposite 
side. The muscle, on each side, arises from the ventral edge of 
the posterior portion of the third basibranchial and from a 
narrow median aponeurosis extending ventralward from it. It 
runs outward and backward posterior to the pharyngo-clavicu- 
lares and is inserted on the ventral surface of the fifth cerato- 
branchial, the surface of insertion extending nearly the full 
length of the bone. At its outer, lateral end a portion of its 
fibres give rise to a tendon which is closely attached to the 
proximal cartilaginous cap of the fifth ceratobranchial, but con- 
tinues across that cap and becomes continuous with a similar 
tendon on the lower end of the adductor of the fifth arch, as 
already described. In 40 mm. specimens the separation of the 
muscle into two parts, one on each side of the head, is equally 
or even more distinctly marked than in the adult, for in young 
