No. 3.] MUSCLES AND NERVES IN AMIA CALVA. 647 
fifth arch consists of a single large piece generally considered 
as a ceratobranchial, and a very small piece of cartilage, usually 
but perhaps not always found attached to its outer dorsal end. 
The piece that I consider as the epibranchial of the fourth arch 
is considered by van Wijhe as the infrapharyngobranchial of 
that arch. Bridge states that there are both an epibranchial 
and a pharyngobranchial in the fourth arch, but he does not 
describe them. 
The hypobranchials (#B./—/V) of the first four arches dimin- 
ish regularly in length from the first to the fourth, the first 
being nearly as long as its ceratobranchial, the fourth only about 
one half as long. The first two hypobranchials closely resemble 
each other in shape, as do also the second two. The first two 
bend sharply inward at their lower ends, and are compressed 
laterally, much as if the end of the bone had been flattened 
dorso-ventrally, and then, after being twisted through some- 
what more than a right angle, had been sharply bent backward 
through about forty-five degrees. This flattened end of the 
element is triangular or wedge-like in shape, and is strongly 
capped with cartilage. The shank or upper portion of the 
element is semi-cylindrical in shape, with its ventral surface 
strongly grooved, the lower end or opening of the groove lying 
in front of the bent and flattened end of the piece. Between 
the shank and the bent end there is, on the anterior and ventral 
edge of each element, a slight process, and on the posterior side 
a slight ridge for the attachment of the strong interarcual 
ligaments that connect each arch with the arch on either side 
of it. 
The most anterior of these ligamenta interarcualia ventralia 
(/2v.h) arises from the dorsal surface of the hypohyal, and forms 
with the others (v./-/V) a nearly straight, though disconnected 
line, running backward and inward from the hypohyal to the 
distal end of the fifth ceratobranchial. The anterior ligament 
is described by van Wijhe in Amia, and by Vetter in Esox, but 
in both cases it is described as passing from the first hypobran- 
chial to the ceratohyal, instead of to the hypohyal as I have 
found it. It is considered by Vetter as a part of the obliquus 
ventralis of the first arch. A similar ligament is found between 
