THE LIZ All D 351 



desert, are vertel)rates in whose skin horny or bony patches 

 are formed. They constantly breathe by means of lungs, and 

 lay large eggs provided with a tough, leathery, or calcareous 



Fig. 330. — Skeleton of a turtle (Cistudo, of Europe), seen from Ix'low, the 

 plastron having been removed and placed at one side. C, rib-plate ; 

 Co, corocoid, a part of the shoulder girdle ; F, filnila ; Fc, femur ; 

 H , humerus ; Jl, ilium ; /.v, ischium ; Pu, pubis ; Pro, pro-coracoid ; 

 R, radius; Sc, scapula; 7', tibia; U, ulna; c, " entoplastron " or inner 

 plate of plastron ; Ep, epiplastron or upper plate ; M, marginal plates ; 

 Nu, nuchal plate ; Py, pygal plates. From Zittel. 



shell. There are about thirty-five hundred species of living rep- 

 tiles, which are grouped into four principal orders as follows : — 

 (1) Turtles, or Chelonia, (2) Lizards, or Sauria, (3) Serpents, 

 or Ophidia, (4) Alligators, or Crocodilina. 



