34 COMPARATIVE ANATOMY AND PHYSIOLOGY. 



this remarkable arrangement is, curiously enough, 

 found also in one species of the amphibian Pelobates, 

 and in the African rodent Lophiomys. 



In the voracious Crocodiles the teeth are con- 

 fined to the maxillae, premaxillrc, and lower jaw, as in 

 Mammals, and these bones are, further, socketed for 

 the reception of the strong teeth. In connection with 

 their mode of life, which requires that they should, 

 while breathing air, hide as much of their body as 

 possible under the water, the anterior nares are 

 placed at the end of their long snout ; the eye, for the 

 same reason, lies high up on the head, and the orbital 

 cavity is seen, therefore, from an upper rather than 

 from a lateral view of the skull ; the hinder openings 

 of the nasal passages, which, in the forms hitherto 

 described, lie in the anterior region of the roof of the 

 mouth, are in the crocodile placed very far back ; this 

 is effected by the development of transverse plates 

 formed by the maxillae, palatines, and pterygoids 

 which unite into a long floor for the nasal passages. 



In many Birds the upper jaw is capable of a 

 certain amount of vertical movement, such as is 

 carried to an extreme in the parrots ; this freedom is 

 due either to incomplete ossification between the 

 ethmoidal and nasal regions, or to the formation 

 of true articulations between the large premaxillse 

 on the one hand, and the frontals, jugals, and pala- 

 tines on the other ; these latter, as in a number 

 of other birds, are not immovably connected with 

 the basisphenoid, but can slide backwards and 

 forwards, while the quadrate, with which the jugal 

 is connected, is movable, as in lizards or snakes. 

 When the quadrate is pushed forwards, as it is when 

 the lower jaw is depressed, it pushes the jugal forwards, 

 and that bone pushes the beak upwards. While the 

 maxillae are comparatively small, the three-rayed pre- 

 maxillae are of considerable size, and the processes by 



