STURCTURE OF TORTOISES. 



31 



Fig. 6. 



9. The bones of the shoulder (o.) articulate on one side with 

 the vertebral column, and with the sternum on the other, so as 

 to form a sort of ring betwixt the carapax and plastrum, through 

 which pass the oesophagus and 

 trachea.* We here observe 

 three branches, which often 

 unite solidly with each other 

 at an early age, and which 

 converge and form by their 

 union, the articular cavity of 

 the humerus. One of these 

 bones, (o.) suspended to the 

 vertebral column, is evidently 

 the scapula ; the second, which 

 is directed backwards, is ana- 

 logous to the coracoid bone of cs 

 birds, and the third, which 

 descends to join the plastrum, 

 is the representative of the 

 clavicle, or at least, the acro- 

 mion process of the scapula, 

 with which this bone ordi- 

 narily articulates. 



10. The pelvis (b.) resembles the ring formed by the bones 

 of the shoulder. 



1 1. The extremities are not very remarkable in the disposition 

 of their bony frame. They are always short ; sometimes they 

 are truncated at the end, and at others flattened and elongated 

 into a paddle ; and in all, the fingers are only slightly moveable, 

 and in general, they are not very distinct externally. 



12. The skin that covers the body of these animals sometimes 

 preserves its softness, and is not covered by scales ; but in almost 

 all of them, it is furnished with a horny layer, of very great con- 

 sistence. These scales form large plates on the carapax and 

 plastrum, the arrangement and aspect of which vary according 

 to the species ; those which cover the carapax of a species of 



^Explanation of the Figure. Skeleton of a Tortoise. (The sternal plas- 

 trum removed to show the interior of the thorax) : t, the head, we, cervical 

 vertebrae, vd, dorsal vertebrae, c, the ribs, anchylosed with the dorsal ver- 

 tebrae to form the carapax, cs, sternal portion of the ribs, or marginal pieces 

 of the carapax, o, scapula, c/, clavicle, co, coracoid bone, 6, pelvis, 

 /, femur, <t, tibia, p, fibula. </, caudal vertebras. 



9. What is the peculiarity of the connexion of the bones of the shoulder 

 with the vertebral column ? 



10. What is the arrangement of the bones of the pelvis? 



11. What is the general character of the extremities 1 



12. What is Tortoise shell ? 



