316 



ZOOLOGY. 



Fig. 273. Tortue Grecque 

 (as seen from below).* 



ribs, and which form in some measure the border of the 

 carapace, evidently represent the sternal portion of these 

 ribs, which in mammalia remain cartilaginous, but which in 

 birds are completely ossified. In 

 some tortoises they remain carti- 

 laginous, and in almost all these 

 animals several of them are supported 

 laterally on the edges of the plastron. 

 The plastron is formed by the ster- 

 num, which presents an extraordinary 

 development, and extends from the 

 base of the neck to the commence- 

 ment of the tail. The bones com- 

 posing it are nine in number, ar- 

 ranged in pairs, and so articulated 

 with each other as to form a great 

 oval plate. The plastron is some- 

 times entire and solid throughout its 

 whole extent, sometimes divided into 

 three portions, of which the anterior 

 and posterior are a little moveable ; 

 at other times it is hollowed out in the centre like a picture- 

 frame. Finally, it is fixed on each side to the carapace by 

 bone or by cartilage. All the muscles and soft parts, as \\cll 

 as the organs, are contained within these two plates. 



The bones of the shoulder (o, cl, co) articulate with the 

 vertebral column on the one hand and the sternal on the other. 

 One of these bones (o) suspending it to the vertebral column is 

 evidently the scapula; a second, directed backwards (co), cor- 

 responds to the coracoid bone of birds ; and the third (cl) 

 represents the clavicle, or at least the acromial process of 

 the scapula, with which it generally articulates. 



The pelvis (b) greatly resembles the osseous girdle formed 

 by the bones of the shoulder ; it is also composed of three dis- 

 tinct pairs of bones : the iliac bone, attached to the transverse 

 processes of the posterior vertebrae of the carapace, a pubis, 

 and ischium directed towards the plastron, and united to the 

 corresponding bones of the other side. 



459. In other reptiles, the bones of the shoulder more 

 resemble those of birds. The limbs generally have nothing 

 remarkable ; sometimes they are truncated at the extremity, 



* Testudo Graeca : Common Tortoise, seen from below. 



