CERATOPSIA CROCODILIA 



431 



SUB-CLASS 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, with fixed quadrate bones, with teeth separately 

 implanted in alveolae and restricted to the upper and lower 

 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, 



i.v. B.V. 



FIG. 103. 1, Atlas and axis of Crocodttus. 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 1} C 2 , first and second centra, formed by the 

 interventralia ; Cp l , Cp z , articular facets of the capitular portions of the first and 

 second ribs ; I. V, interventral ; JVj, N%, first and second neural arch, formed by 

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

 zygapophysis ; R lt Ry, ribs ; Sp, detached spinous process of the first neural arch ; 

 ti, t%, facets of the tubercular portions of the first and second ribs ; 1, 2, intercentra 

 = basiventralia ; 2 (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, quadra to-jugal 

 arch. The possession of a longitudinal cloacal opening and of 



