No. 3.] MUSCLES AND NERVES IN AMIA CALVA. 645 
middle bony portion of the element there is a similar articular 
cup for the articular end of the second hypobranchial. The 
bony portion of the element is much constricted in its middle 
portion, both dorso-ventrally and laterally, the dorsal surface of 
the piece being, however, left nearly its full and even width, so 
that the piece in section is V-shaped, or even T-shaped. At 
the hind end of its ventral edge there is, on either side, a roll- 
like projection directed backward, outward, and downward. 
The posterior cartilaginous portion of the element is shorter 
than either of the other portions, is V-shaped or T-shaped in 
section, the broad surface above, and on either side, at the 
extreme front end of its ventral edge, it projects outward and 
forward, and caps the ends of the roll-like projections on the 
hind end of the bony portion of the element. From each of 
these processes arises a short, tough, conical ligament which is 
inserted on the end of a cylindrical process of the third hypo- 
branchial, the body of that hypobranchial articulating with the 
basibranchial in a very slight depression at the anterior end 
of its dorsal edge. 
The second basibranchial has somewhat the shape of a short, 
slightly curved T-rail, the flat surface of the rail presented 
dorsally on the outside of the curve, and the ventral edge 
thickened slightly at its front end, where it gives attachment 
to a short, tough ligament similar to the one found on the pre- 
ceding element. This ligament connects with a process of the 
fourth hypobranchial, the body of that hypobranchial articulat- 
ing with the basibranchial near its dorsal edge, in the same 
way and manner that the third hypobranchial articulates with 
the preceding element. 
The third basibranchial lies in a continuation downward and 
backward of the curved line of the second basibranchial. It is 
strongly T-shaped in section, and ends in a long, prow-like 
point, directed backward and lying about on a level with the 
ventral edge of the first basibranchial. This gives to the 
element a keel-shaped appearance, the edge of the keel below, 
with a strong angle at about the middle of its length. 
The first and second basibranchials are strongly connected 
by ligament, the ligament continuing backward along the ven- 
