274 



INTEODUCTIOX TO ZOOLOGY. 



the body enclosed between two shields, with apertures for the 

 head, the tail, and the four legs. The jaws are horny and 

 without teeth. 



If we look upon one of the common Land Tortoises, slowly 

 pacing along, and clad in its unyielding armour, we are in- 

 clined to ask, " Why should it be called a vertebrate animal ? 

 Where are the vertebrae and the ribs ? " 



If we examine the under side of the shield that covers 

 the back of the animal {Fig. 233), the question may with 

 ease be answered. The structure of that shield — or, as it 

 is termed, the carapace — reveals the vertebrae and ribs, but 



Fig. 233.— Skkleton of Tortoise.* 

 • Fift. 2oo.— Skeleton of L,\nd Toktoisr with tlie jjlastron or lower shell re- 

 moved.— if, cervical vertebraj; i/t', linrsiil vcitebrx; r, ribs; sr, sternal ribs, or mar- 

 ginal pieces of the carapace; o, scapula; c/, clavicle; co, coracoid bone; p, pehis; 

 '', femur; t, tibia;/, tibula. 



