TEETH OF REPTILES. 



395 



extending along the palatines and pterygoids. The genus Oli- 

 yodon appears to form the sole exception to this rule. In the 

 Dryinus nasutus, a few small teeth are present on the ecto- 

 pteiygoid as well as on the pterygoid. 



In Dryophis, Dipsas, and Bucephalus, in which the maxillary 

 teeth increase in size towards the posterior part of the bone, the 

 large terminal teeth of the series are traversed along their anterior 

 and convex side by a longitudinal groove. In the Bucephalus 

 capensis, the two or three posterior maxillary teeth present this 

 structure, and are much larger than the anterior teeth, or those of 

 the palatine and premandibular series. They add materially, 

 therefore, to the power of retaining the prey, and may conduct into 

 the wounds which they inflict an acrid saliva ; but they are not 

 in connection with the duct of an express poison-gland. The 

 long grooved fangs are either firmly fixed to the maxillary bones, 

 or are slightly moveable, according to their period of growth. 

 They are concealed by a sheath of thick and soft gum, and their 

 points are directed backward. The sheath always contains loose 

 recumbent grooved teeth, ready to succeed those in place. 



In most of the Colubri, each maxillary and premandibular bone 

 includes from twenty to twenty-five teeth. They are less numerous 

 in the genera Tortrix and Homalopsis, and are reduced to a still 

 smaller number in the poisonous serpents, in the typical genera 

 of which the short maxillary 

 bone supports only a single 

 perforated fang. 



The maxillary, fig. 268, e, 

 diminishes in length with the 

 decreasing number of teeth 

 which it supports : the ecto- 

 pterygoid, d, elongates in the 

 same ratio, so as to retain its 

 position as an abutment against 

 the shortened maxillary ; and 

 the muscles implanted into 

 the ectopterygoid communicate through it to the maxillary 

 bone the hinge-like movements backward and forward upon the 

 ginglymoid articulations connecting that bone with the prefrontal 

 and palatine bones. As the fully developed poison-fangs are 

 attached by the same firm basal anchylosis to maxillary sockets, 

 which forms the characteristic mode of attachment of the simple 

 or solid teeth, they necessarily follow all the movements of the 

 superior maxillary bone. When the external pterygoid is re- 



268 



Structure of the poison-teeth of the Rattle-snake 



