266 



REPTILIA. 



Fig. 177. 



Skeleton of Tortoise. 



A, superior maxilla ; B, inferior maxilla ; c, ossiculnm auditus ; D, os hyoides ; E, cervical vertebra ; F, 

 dorsal vertebra ; G, sacrum ; H, caudal vertebras ; i, dorsal ribs ; ic, marginal scales ; N, scapula ; o, 

 coracoid bone ; p, os humeri ; Q, radius ; E, ulua ; s, bones of the carpus ; T, metacarpal bones ; u, digital 

 phalanges ; V, pelvis ; w, femur ; x, tibia ; Y, fibula ; z, tarsus ; AS., metatarsus ; A.V., phalanges of the 

 foot. 



case filled up with a cartilaginous membrane. 

 In the carapax of fresh-water tortoises (Emys), 

 and in the Chelides, the interspaces between 

 the ribs in time become completely rilled up, 

 and the ribs are connected by suture, through- 

 out their whole extent, to each other and to 

 the marginal pieces (K). 



The marginal pieces (fg. 177, p) form a sort 

 of osseous frame composed of a series of bones, 

 eleven in number on each side, which are 

 united together liy suture, and likewise con- 

 nected with the extremities of the ribs. In 

 the Tortoises this connection with the ribs 

 is effected by suture, but in the Turtles and 

 other genera having the extremities of the 

 ribs narrow, their apices are implanted in 

 fossae excavated in the marginal plates, where 

 they are fixed by a species of synchondrosis. 



These marginal plates cannot be otherwise 

 regarded than as the representatives of the 

 sternal ribs of the Crocodiles and other 

 Saurians ; the two first and the two last, like 

 the abdominal ribs of the Crocodile, being de- 

 veloped without the presence of any dorsal 

 ribs in correspondence with them. In the 

 Soft-Tortoises (Trionyx) the marginal pieces 

 are never ossified, but are represented by a 

 cartilaginous rim, in which sometimes osseous 

 particles are sparingly deposited. 



The ventral cuirass of the Clielonian rep- 

 tiles, called the plastrum, is exclusively formed 

 by the sternum, which in this race of animals 

 seems to attain its maximum of development. 

 It consists invariably of nine pieces, eight of 



which are pairs; while the ninth, situated 

 between the four anterior ones, is central and 

 azygos. 



These elements of the sternum have been 

 well-named by Geoffroy St. Hilaire in ac- 

 cordance with the situations that they occupy. 

 The anterior pair are the episternal pieces, and 

 the pair situated behind tliese the hyo-sternals, 

 In the centre bounded by the above four 

 bones is the azygos piece named the ento- 

 sternal. The pair situated immediately pos- 

 terior to the hyosternal are called the hypo- 

 sternal pieces, and the two which terminate 

 the plastrum xipho-sternals. The sacral and 

 caudal vertebras return to the usual arrange- 

 ment, being all free and moveable, having 

 their bodies concave in front and convex be- 

 hind, and their apophyses as in ordinary ver- 

 tebrae. Their number varies in different 

 species from eight to twenty-seven. 



The scapular apparatus is contained in the 

 interior of the thoracic cavity. It consists 

 of a remarkably shaped three-branched bone 

 (Jig. 178.), which is suspended on each side by 

 a ligamentous attachment beneath the second 

 vertebra of the carapax. The branch which 

 is thus suspended ( ), notwithstanding its 

 strange position inside the thorax, is the 

 scapula ; the branch b Cuvier, after the nia- 

 turest deliberation, decided to be its acromion 

 process ; while the flattened bone c directed 

 backwards, he considers as being incontest- 

 ably the coracoid bone. This three-branched 

 shoulder, with its almost cylindrical scapula, 



