3o() ZOOLOGY SECT. 



strongly recurved, so tliat they have the character of sharp 

 hooks, their function being rather to hold the prey and 

 l^revent it slipping from the mouth while being swallowed 

 than to masticate it. Non-venomous Snakes possess only 

 teeth of this character. In the venomous Snakes more or 

 fewer of the maxillary teeth assume the cliaracter of poison-fangs. 

 These are usually much larger than the ordinary teeth and either 

 grooved or perforated by a canal for the passage of the duct of the 

 poison-gland. In the Vipers (Fig. 980) there is a single large 

 curved poison-fang with small reserve-fangs at its base, these being 

 the only teeth borne by the ma.Killa', which is very short ; in the 

 venomous Colubrine Snakes the poison-fangs are either the most 

 anterior or the most posterior of a considerable range of maxillary 

 teeth. In the Vipers the large poison-fang is capable of being rotated 

 through a considerable angle, and moved from a nearly horizontal 

 position, in which it lies along the roof of the mouth embedded 

 in folds of the mucous membrane, to a nearly vertical one, when 

 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 svith the palatine and transverse. In 

 Sphenodon (Fig. 990) 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 cliaracter, bite in between these two upper 

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

 as to furm continuous ridges. Each premaxilla bears a j^romiuent, 

 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-maxilke, the maxillas, and the 

 dentary. They are large, conical, hollow 'teeth devoid of roots, 

 each lodged in its socket or alveolus (thecodont), and each 

 becoming replaced, when worn out, by a successor developed on 

 its inner side. 



A bifid tonffue 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 aj^pendages behind. The 

 Monitors (Fig. 999, A) have forked retractile tongues like those of 

 Snakes. The tongue of the Chamadeons 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 



