CERATOPSIA CROCODILIA 



431 



Sub-Cla ss VI. — CROCODILIA. 



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

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

 tailed reptiles, vnth fixed quadrate hones, loith teeth separately 

 implanted ^Vi alveolae and restricted to the uj^per and loioer 

 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, 



Fig. 103. — 1, Atlas and axis of Crocndilvs. 2, Atlas aud 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 gastroceutrous vertebra. Az, Anterior zygapophysis ; B.D, 

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

 iuterventralia ; Cp^, Gp^, articular facets of the capitular portions of the first and 

 second ribs ; /. F, interventral ; N-^, JV^, first and second neural arch, formed by 

 the basidorsalia {B.D in 4); Od, odontoid proeess = first centrum ; Pz, posterior 

 zygapophysis ; 7?,, B^^ ribs ; Sp, detached spinous jirocess of tlie first neural arch ; 

 ti, to, facets of the tubercular portions of the first and second ribs ; 1, 2, iiitercentra 

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

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

 the 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, bony, quadrato-jugal 

 arch. The possession of a longitudinal cloacal opening and of 



