XIII 



PHYLUM CHORDATA 



331 



the Snake opens its mouth to strike its prey. The rotation of 

 the maxilla is brought about by the backward or forward move- 

 ment of the pterygoid with the palatine and transverse. 



In Hatteria (Fig. 934) there are pointed, triangular, laterally- 

 compressed teeth, arranged in two parallel rows, one along the 

 maxilla, the other along the palatine. The teeth of the lower jaw, 

 which are of similar character, bite in between these two upper 

 rows, all the rows becoming worn down in the adult in such a way 

 as to form continuous ridges. Each pre-maxilla bears a prominent, 

 chisel-shaped incisor, represented in the young animal by two- 

 pointed teeth. In the young Hatteria a tooth has been found on 

 each vomer a condition exceptional among Reptiles. 



In the Chelonia, teeth are entirely absent, the jaws being 

 invested in a horny layer in such a way as to form a structure 



like a Bird's beak. 



The Crocodilia have numerous teeth which 



are confined to the pre-maxillse, the maxillae,. 



and the dentary. They are large, conical ,. 



B 



FIG. 942. A, tongue of Monitor indicus. B, tongue of Emys europsea. C, tongue of 

 Alligator. L, glottis ; M. ^ mandible ; Z, tongue ; ZS, tongue-sheath. (From "Wiedersheim's 

 ii-e A natomy.) 



hollow teeth devoid of roots, each lodged in its socket or alveolus, 

 (tlucodont) and each becoming replaced, when worn out, by a 

 successor developed on its inner side. 



A bifid tongue like that of Lacerta occurs in several families of 

 Lacertilia. Others have a thick, short tongue, undivided in front 

 and often provided with two long appendages behind. The 

 Monitors (Fig. 942, A) have forked retractile tongues like those of 

 Snakes. The tongue of the Chameleons is an extremely remark- 

 able organ ; it is of sub-cylindrical form with an enlarged extremity, 

 and is so extensile that it is capable of being darted out to a 

 distance sometimes equalling or even exceeding the length of the 

 trunk ; this protrusion can be effected with lightning-like rapidity : 

 and it is in this way that the animal catches the Insects which 



