CROCODILIA 



197 



above the pharynx, and not, as in other reptiles — save the imme- 

 diate ancestors of the mammals — entering the mouth at the front 

 end. This peculiar arrangement of the air-passages, so like that of 

 ourselves, has much to do with the water habits of the crocodiles, 

 as we shall see. 



The teeth are conical in shape, and are always restricted to the 

 edges of the jaws, above and below. They are inserted deeply and 



Fig. gg Fig. 100 



Fig. 99. — Skull of Alligator mississippiensis, from below. 



Fig. 100. — ^The same, from above: bo, basioccipital; bs, basisphenoid; /, frontal; 

 y, jugal; /, lacrimal; m, maxilla; », nasal; ^, parietal; ^a, palatine; ^j», premaxilla; 

 pf, prefrontal; pr, postfrontal; pt, pterygoid; q, quadrate; gj, quadratojugal; tr, 

 transverse. 



firmly in sockets, and are replaced frequently by new ones growing 

 beneath them, pushing the older ones out as their usefulness becomes 

 impaired by injury or by use. In some species there are as many as 

 thirty teeth in each side of the jaws, above and below, although the 

 broad-headed kinds have a smaller number. 



The neck is short, as has been stated, but it always includes 

 in living forms nine vertebrae, a number probably slightly in excess 

 of that of their terrestrial forbears. By the pecuhar mode of 



