370 EDWARD PHELPS ALLIS, JR. 
POLYODON 
Bridge (’79) considered the cartilages in the upper jaw of this 
fish to be similar to those in the upper jaw of the Selachii, and 
he says that these cartilages of all these fishes are pterygoquad- 
rates, without ‘‘even rudiments of recurrent palatine out- 
growths,” the palatine being considered by him to be a preoral 
_ structure. It nevertheless seems best to refer to the upper jaw 
of this fish as a palatoquadrate, that being the term usually 
applied to it in the Selachii. 
In the one adult specimen of Polyodon that I have examined, 
and also in three young specimens 154 to 300 mm. in length, I 
find the external surface of the palatoquadrate looking laterally 
in its posterior portion, as Bridge states, and anterodorsally in 
its anterior portion. Its quadrate portion has the leaf-like out- 
growth that Bridge describes and calls its orbitar process, this 
process projecting forward lateral to the musculus adductor 
mandibulae. The hind end of the so-called maxillary splint is 
closely applied to the external surface of the orbitar process, the 
surface of the process being slightly excavated to receive it. 
For a certain distance anterior to the anterior end of the orbitar 
process, the maxillary splint is not in contact with the palato- 
quadrate, but farther forward its dorsal edge is V-shaped, fits 
closely upon the ventrolateral edge of the palatoquadrate, and 
so extends to the point where that cartilage articulates, in the 
median line, with its fellow of the opposite side of the head. 
The anterior portion of the ventral edge of the splint is furnished 
with small teeth, and, extending approximately the same dis- 
tance along the dorsomesial edge of the palatoquadrate, there is 
a row of somewhat stronger teeth. The bone to which these 
latter teeth are attached fits closely upon the related edge of 
the palatoquadrate, and although fused anteriorly with the 
pterygoid splint of Bridge’s descriptions, it has markedly the 
appearance of being of independent origin. It is called by 
Gegenbaur (’98, p. 342) the palatine, but it is to be noted that 
it is, even in my quite young specimens, definitely of membrane 
origin, and that it lies along the dorsomesial, instead of the 
