THE SKULL OF REPTILES 8 1 



either cylindrical throughout or partly or chiefly flattened and denti- 

 culated. The first two or three teeth on each side, especially above^ 



Fig. 66. Phytosaur skull: Machaeroprosopus, from above and from below. 



are cylindrical and much elongated. The dentulous portion of the 

 premaxillae is long, with twenty or more teeth on each side. 



The chief differences in the skull structure of the various members- 

 of the order are found in the relative position of the external nares^ 



