CLASS REPTILIA 



529 



(Fig. 440) is very firm. It is devoid of teeth. The pre- 

 maxillae (pmx), maxillae (mx), and dentary bones possess sharp 

 edges which are covered with horn, and form a beak. The 

 quadrate bone (g) is stationary; no transverse bone is present 



FIG. 439. Skeleton of a turtle, Cistudo lutaria, ventral aspect; plastron 

 removed to one side, c, costal plates; co, coracoid; e, entoplastron; ep, epi- 

 plastron; /, fibula; fe, femur; h, humerus; hpp, hypoplastron; hyp, hyoplas- 

 tron; jl, ilium; js, ischium; m, marginals; nu, nuchal; pb, pubis; psc, precora- 

 coid; py, suprapygal; r, radius; sc, scapula; /, tibia; u, ulna; xp, xiphiplastron. 

 (From Zittel.) 



as in other reptiles ; there is one occipital condyle, and only one 

 sphenoidal bone, the basisphenoid (BSph). The supraoccipital 

 (so) has a prominent crest. 



There are comparatively few vertebra (Fig. 439) usually 

 eight cervical, ten thoracic, two sacral, and a variable number of 

 caudal. The vertebrae of the neck move very freely upon one 



2 M 



