431 



COMPARATIVE ANATOMY. 



Fig. 226. Cervical 

 vertebra of Vultur 

 cinereus. c Centrum. 

 p Arch, s Spinous pro- 

 cesses. CO Eudimen- 

 tary rib. 



Eeptilia and Aves ribs are found along the whole of the dorsal 

 portion of the vertebral column, and are absent only in the Chelonii. 



The movable cervical ribs of the Reptilia 

 unite with the vertebra in the Aves (Fig. 226, 

 co), and the two together bound a foramen 

 trans versarium . 



In the caudal region of the column of the 

 Saurii, Chelonii, and Crocodilini we meet with 

 inferior arches, which are always attached be- 

 tween two centra, and take part in the forma- 

 tion of a caudal canal. They are rudimentary 

 in Birds. The inferior processes of the Ophidii, 

 Saurii, and Aves, which are given ofE directly 

 from the centra, are quite different from these. 

 On comparing the vertebral column of the 

 Reptilia and Aves with that of the Amphibia we can see that it is 

 divided into a larger number of regions. A cervical and a lumbar 



region are more 

 distinctly marked 

 off, owing to the 

 connection between 

 a number of ribs 

 and a sternum. The 

 lumbar region con- 

 tains the pre-sacral 

 group of vertebrte, 

 which have only 

 short ribs ; it is dis- 

 tinct in the Saurii 

 and Crocodilini. 

 The absence of any 

 sternal connections 

 in the Ophidii is 

 the cause of there 

 being no difference 

 between the tho- 

 racic and cervical 

 regions in these 

 forms, as well as 

 of the impossibility 

 of distinguishing a 

 lumbar one. In the 

 Chelonii also the 

 vertebrte of the 

 trunk are similar in 

 character through- 

 out. These regions 

 are not, however, 

 very sharply marked off from one another, inasmuch as in the Saurii 



Fig. 227. Sacral por. Fig. 228. Sacral portion of 

 tion of the vertebral the vertebral column of a bird, 

 column of a Reptile, 

 ■with the adjacent pre- 

 andpost-sacral vertebrae. 



Both of these diagrammatic figures are drawn as if from 

 the ventral surface, and show the nervous plexus on the 

 left. In both the figures a is the first sacral vertebra, b the 

 second sacral vertebra. . . . 1, 2, 3, 4 Presacral. 1', 2',3',4' 

 .... Post-sacral (or caudal) vertebrae. 



