VERTEBRJi: OF THE TORTOISE. 129 



lu the figure of the skeleton of tlie box-tortoise (Fig. 

 20) a section of the carapace and plastron has been re- 

 moved from the right side to expose the dorsal and 

 sacral vertebrae, and the disposition of the scapular and 

 pelvic arches. The eight cervical vertebrae are free, 

 movable, and ribless ; the fourth of these vertebrae has 

 a much elongated centrum, which is convex at both 

 ends; the eighth is short and broad, with the anterior 

 surface of the body divided into two transversely elon- 

 gated convexities, and the posterior part of the body 

 forming a single convex surface divided into two lateral 

 facets ; the under part of the centrum is carinate. The 

 neural arch, which is anchylosed to this centrum, is 

 short, broad, obtuse, and overarched by the broad ex- 

 panded nuchal plate, cli. The first dorsal vertebra, d 1, 

 is also short and broad, with two short and thick pleura- 

 pophyses, articulated by one end to the expanded ante- 

 rior part of the centrum, and united by suture at the 

 other end to the succeeding pair of ribs. The head of 

 each rib of the second pair is supported upon a strong 

 trihedral neck, and articulated to the interspace of the 

 first and second dorsal vertebrae: it is connate, at the 

 ]Dart corresponding to the tubercle, with the first broad 

 costal plate, which articulates by suture to the lateral 

 margin *of the first neural plate, and to portions of the 

 nuchal and third neural plates : the connate rib, which is 

 almost lost in the substance of the costal plate, is con- 

 tinued with it to the anterior and outer part of the cara- 

 pace, where it resumes its subcylindrical form, and arti- 

 culates with the second and third marginal pieces of the 

 carapace. The neural arch of the second dorsal vertebra 

 is shifted forwards to the interspace between its own cen- 

 trum and that of the first dorsal vertebra. A similar 

 disposition of the neural arch and spine, and of the ribs, 



