330 



ZOOLOGY 



SECT, 



rarely developed on the pre-maxillse, but are present on the 

 maxillse, palatines, pterygoids, and sometimes the transverse bones, 

 as well as the dentary of the mandible. They may be of the same 

 character throughout, solid elongated sharp-pointed teeth, which 

 are usually strongly recurved, so that they have the character of 

 sharp hooks, their function being rather to hold the prey and 

 prevent 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 

 character of poison-fangs. 

 These are usually much larger 



FIG. 941. Tarsus of Crocodile (right side) 

 from above. F. fibula ; T. tibia ; t. i. <: the 

 astragalus formed of the united tibiale, 

 intermedium and centrale ; /. fibulare 

 (calcaneum) ; 1 3, united first, second 

 and third distal tarsals ; 4, fourth tarsal ; 

 I IV, first to fourth metatarsals ; V?, fifth 

 distal tarsal and fifth metatarsal. (From 

 Wiedersheim.) 



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. 933) there is- 

 a single large curved poison- 

 fang with small reserve-fangs at 

 its base, these being the only 

 teeth borne by the maxilla, 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 



FIG. 940. Pelvis of young Alligator, ventral 

 aspect. B, fibrous band passing between the 

 pubic and ischiadic symphyses ; BR. last pair 

 of abdominal ribs ; F. obturator foramen ; 

 G, acetabulum ; 11 ilium ; Is. ischium ; M. 

 fibrous membrane between the anterior ends 

 of the two innominate bones and the last pair 

 of abdominal ribs ; P. pubis ; Sy. ischiadic 

 symphysis ; /, //, first and second sacral 

 vertebrae. (From Wiedersheim.) 



