CROCODILIANS, LIZARDS, AND SNAKES. 691 



In all genera the ])alatine bono is longitudinal and compressed except 

 in the Scolecophidia, where it is so short as to be transverse. The 

 pterygoids are elongate and extend to the quadrate except in the 

 Scolecophidia. In the Opoterodonta they are cyliudric, and extend 

 beyond the quadrate, while in the Epanodonta they are flattened and 

 do not quite reach the latter. They are generally compressed so as to 

 present a vertical lamina, but in peropodous genera, especially in those 

 with basipterygoid processes, they are expanded inward so as to be 

 horizontal. They are also horizontal in Xenopeltis. The compressed 

 form is related to the greatest mobility, and is hence most developed 

 in the Solenogiypha. Ectopterygoids are present in all the super- 

 families except the Scolecophidia. They are longest where the maxil- 

 laries are shortest, that is, in the Solenoglypha. 



The mandible in Serpentes always lacks the surangular bone, and 

 the angular is small and far anterior to the angle of the jaw, which is 

 formed by the articular. The coronoid is absent, excepting in the Scole- 

 cophidia, Tortricina, and Peropoda, except Charina, where it is want- 

 ing. The splenial is always present, and is internal exclusively, except 

 in Typhlops, where it is more extensively developed on the external than 

 on the internal side, leaving the dentary but a narrow strip. In Ti/ph- 

 lojjs also the angular is a very small splint, between the splenial and 

 the base of the coronoid on the external side of the jaw. The Meckel- 

 ian groove is open in many snakes, and in others it is closed by the 

 apposition of the edges <^»f the dentary and splenial bones. In some 

 species it is open only for a short distance. It is open in Crotalidai, 

 Yiperid;e, and Hydrophida-, and in Ilysiida', Boidie, Pythonida?, Chari 

 nidii', and Xenopeltida?. It is also open in the following genera of 

 Colubrid*: Natrix, Eiitfcnia, Heterodon, Coluber^ Ophiholus^ Dlailophis, 

 Cycloj/his, Liopeltis, Salvadora, Rhinochilus, Haldea^ Virginia, Storeria^ 

 Ahastor and Farancia. In Osceola it is partly open; while it is closed 

 in T}iphlops, Elaps, Causns, Sibon, Spilotes, Bascanium, and Carpho- 

 phiops. Thus the open groove is ijrobably characteristic of Crotalidoe, 

 Yiperida', Hydrophidce, the Peropoda, and the Ilomalopsinae. Further 

 than this no definite boundaries can be yet traced by it. 



THE DIGESTIVE SYSTEM. 



The teeth of snakes are not furnished with roots, and are not sunk 

 in alv^eoli, but their bases are coossitied with the bones which bound 

 the mouth. They have simple, acutely conic crowns with an oval sec- 

 tion, sometimes with a sharp angle posteriorly when a cutting edge is 

 present. In certain genera (Opisthogly]>ha) there is a groove on the 

 anterior or external face {Ogmii(s) of the posterior one or two teeth of 

 the maxillary bone. In one genus all the maxillary teeth are grooved 

 (Ogmodon); while in the venomous species it is the anterior teeth 

 which have undergone modification. In the Proteroglypha the anterior 

 tooth is deeply grooved on the anterior face, and the edges of the 

 groove have grown forward and inward so as to be in contact, thus 



