No. 472] ANATOMY OF CRYPTORRANCHUS 289 



The bony cranium will first be described, and then a brief 

 description of the cartilaginous cranium will be given. 



The premaxillce, forming the extreme anterior tip of the skull, 

 are firmly united w^th each other in the middle line, and articulate 

 less closely, on each side, with the adjacent maxilla^. Their dorsal 

 surface is prolonged backward somewhat, to articulate with the 

 anterior borders of the nasals. Between them, in the mid-dorsal 

 line, is a small foramen, and each of them exhibits a small fora- 

 men on its anterior surface (Fig. 1, P. Mx.). Their antero-ventral 

 border is armed with the teeth above mentioned, while the postero- 

 ventral border articulates with the anterior border of the vomers 

 (Fig. 2, P. Mx., v.). About half of the median border of the 

 nasal opening (iY.) is formed by the premaxilla. 



The two maxillary bones (Mx.) form the rest of the upper jaws, 

 and make up, in fact, about three fourths of their extent. Their 

 entire ventral border is armed, as has been described, with a single 

 row of teeth. The medial end of their arc is in articulation with 

 the premaxillary, while the lateral end tapers somewhat and is 

 connected with the anterior angle of the pterygoid by a tough 

 band of connective tissue. On the dorsal aspect of the maxillary, 

 near the medial end, a triangular projection extends in a postero- 

 medial direction between the frontal and the prefrontal. On the 

 anterior border of each maxilla, at the base of the triangular pro- 

 jection just described, are two small openings, the infra-orbital 



I1ie nasals (Figs. 1 and 3, Xa.) lie just back of the premaxillse 

 and form the posterior half of the median border of the anterior 

 nares (N.). The two bones, when taken together, have somewhat 

 the shape of an arrowhead, the tip of the head pointing towards 

 the base of the skull. The base of the arrowhead articuhites 

 anteriorly with the posterior projections of tlic |)iH>ni;i\ill;t' that 

 have already been mentioned. In the nil(l-<l(>r>al \\uv the two 



lateral borders articulate with the frontal Ixmcs. 1 hr anterior 

 half of each nasal is closelv unite.l, ventrally. with the .loi-al >i(U^ 

 of the correspoiKhng vomer, and thus lieli)S to form the .sei>tiun 

 between the two nasal ciuimbers. 



The jrontals ( /•'.) are two large, much elongated bones that lie 



