362 



SAUEOPSIDA. 



instance, the Connnuu luiglish Adder, which may retain the ova 



in the uterus until they are incubated. 



Many Eeptilia are proviJeil with numerous teeth, some being 



connected with poisonous glands 

 at their base (fig. 204, u). The 

 poison-fangs have a tube run- 

 ning up tliem, through which 

 the jioison is ejected when the 

 snake bites. Teeth of reptiles, 

 except in the Crocodiles (fig. 

 203, i and ii), are not lodged 

 in sockets, as we see is the case 

 in the IMamnialia, but are im- 

 planted in one long groove near 

 the edge of the jaw. 



There are four existing 



groups of Tieptiles — namely, tlie Clirhmia, or Tortoises and 



Turtles; the Lacriiilia, or Lizards; the Oj^ihidia, or Snakes; 



. 203. — Plkurodont and Acrodont 



DENTJTjriN, 



i, Pleurodont dentition (in crncodilrs, 

 &c.); ii, acrodont dentition (note teflii 

 ancliylosed to the bone). (Brit. Mii^. 

 Guide.) 



,1, Ilt'ad ol' .nlder ; B, (if grasH-snjiko 

 /', poi.son-baj,' ar.tl fang. 



IlE \ri OF Rkptit.ks. 



; f, side view of .1 .- r, j^ni-^.m Hii 



and the dronnii/ia. or Crocodiles and .Vlligators. Xumerous 

 extinct forms arc fouiiil in the i\lesozoic or Secondary rocks, 

 a period of the earth which was characterised by the abundant 

 and extravagant forms of reptilian life. The British Eeptilia are 



