CERATOPSIA — CROCODILIA 



431 



Si 11- Cla ss 1 7. — CROCODIL IJ. 



If we had to deal only with tlie recent Crocodilia the follow- 

 ing would be an all sufficient diagnosis : — Four footed, long- 

 tailed reptiles, vnth fixed quadrate hones, with teeth sejiarately 

 implanted in alveolae and restricted to the upj^er and loiver 

 jaws. 



To define Crocodilia in general and to distinguish them from 

 various extinct groups we have to resort to additional characters. 

 The vertebrae are solid : the ribs of the neck and thorax possess 

 a distinct capitulum and tuberculum ; there is a series of loose, 



B.D 



Fig. 103. — 1, Atlas and axis of Crocodilvs. 2, Atlas and axis of Metriorhynchus, a 

 Jurassic Crocodile, see p. 439. 3, Analysis of the first two cervical vertebrae of a 

 Crocodile. 4, Diagram of the fundamental composition of a Reptilian or other 

 Amniotic, typically gastrocentrous vertebra. Az, Anterior zygapophysis ; B.D, 

 basidorsal ; B. V. basiventral ; C-^, tU, first and second centra, formed by the 

 interventralia ; Qj\ C/r, articular facets of the capitular portions of the first and 

 second ribs ; /. T', interventral ; iVj, N.r, tirst and second neural arch, formed by 

 the basidorsalia {B.D in 4); Od, odontoid process = first centrum; I'z, posterior 

 zygapophysis ; B^, Ji.2, ribs ; .S);, detached spinous process of the first neural arch ; 

 t'l, t.^, facets of the tubercular portions of the first and second ribs ; 1, 2, intercentra 

 = basiventralia ; - (in 3), second basiventral "complex or iiitercentrum," continued 

 upwards as a meniscus or intervertebral pad ; /, //, III, position of the exit of 

 tlie first, second, and third spinal nerves. 



compound abdominal ribs; the humerus is devoid of an ent- 

 epicondylar foramen ; the iliac bones are broadened out and 

 attached to two sacral vertebrae ; the pubic bones are simple, 

 not bifurcated, and neither they, nor the ischia are ventrally 

 united. The skull always has a strong, l)ony, quadrato-jugal 

 arch. The possession of a longitudinal cloacal opening and of 



