130 VERTEBRA OF THE TORTOISE. 



prevails in the tliird to the ninth dorsal vertebra inclu- 

 sive. The corresponding seven neural plates are connate 

 with the spines of those vertebras, and form the major part 

 of the median pieces of the carapace ; the correspondiug 

 costal plates, anchyclosed to the ribs, form the medio- 

 lateral pieces ; the ninth, tenth, and pygal plates, with the 

 marginal plates of the carapace, do not coalesce with any 

 parts of the endoskeleton. The bony floor of the great 

 abdominal box, or " plastron," is formed by the haemapo- 

 physes and sternum connate with dermal osseous plates, 

 forming, as in the turtle, nine pieces, one median and sym- 

 metrical, answering to the proper sternum, and eight in 

 pairs: but they are more ossified, and the hyo and hypo- 

 sternals unitQ suturally with the fourth, fifth, and sixth 

 marginal plates, formi^ the side-walls of the bony cham- 

 ber. The junction between the hyo- and hyposternals 

 admits of some yielding movement. The iliac bones, 62, 

 abut against the pleurapophyses of the tenth, eleventh, 

 and twelfth vertebrae, counting from the first dorsal ver- 

 tebra. These three vertebrae form the sacrum : their pleu- 

 rapophyses are unanchylosed, converge, and unite at their 

 distal extremities to form the articular surface for the 

 ilium. Beyond these the vertebrae, thirty-five in number, 

 are free, with short, straight, and thick pleurapophyses, 

 articulated to the sides of the anterior expanded portions 

 of the centrums. They diminish to mere tubercles in the 

 first caudal vertebra, and disappear in the remainder. The 

 neural arches of the caudal vertebra are flat above, and 

 without spines. The strong columnar scapula, 51, is 

 attached by ligament to the first costal plate, and, retain- 

 ing its primitive rib-like form, it descends almost vertically 

 to the shoulder-joint, of which it forms, in common with 

 the coracoid, 52, the glenoid cavity. ,A stroug subcylin- 

 drical process or continuation of the scapula, representing 



