144 VERTEBRATE ZOOLOGY 



The endoskeleton is made up of the axial skeleton, which in- 

 cludes the skull and the vertebral column and ribs, and the ap- 

 pendicular skeleton, which includes the framework of the limbs 

 and the girdles by means of which they are firmly attached to 

 the trunk. The limbs and their girdles are between the right and 

 left rows of ribs in turtles ; in all other vertebrates they lie exter- 

 nal to the ribs. 



The Axial Skeleton. Disarticulate the neck and remove it, with 

 the head, from the carapace. Disarticulate and remove also the 

 pectoral and pelvic girdles with the legs, and the tail. 



The vertebral column contains three regions,— the neck, trunk, 

 and tail. The trunk region consists of the vertebrae and the ribs, 

 which enter into the formation of the carapace. It will be first 

 studied. 



The Carapace. Boil the carapace until the flesh still remaining 

 on it can be easily removed. Care must be taken not to boil it so 

 long that it will fall to pieces. Peel off the horny plates and note 

 that they do not coincide with the bony plates beneath. Observe 

 the arrangement of the bony plates as seen on the outer surface. 

 Note which of these plates are fused with the trunk vertebrae and 

 which with the ribs. 



The medial row of plates is composed of the single anterior 

 nuchal plate, followed by a row of vertebral plates with each of 

 which is fused the dorsal portion of a vertebra, and one or more 

 posterior pygal plates. At each side of the medial row is a row of 

 costal plates, with which the ribs are fused; and lateral to the 

 costal plates are the marginal plates. 



Exercise 18. Make an outline drawing of the dorsal surface of the 

 bony plates of the carapace. 



Study the inner surface of the carapace. Note the centra of the 

 vertebrae which project beneath the vertebral plates with which 

 they are fused. Note also the ribs, which are fused with the costal 

 plates. Note the difference between the first pair of ribs and those 

 following. The last two vertebrae form the sacrum, which supports 

 the hinder extremities. 



