142 



BEGINNERS' ZOOLOGY 



The Skeleton (Fig. 267). — The carapace is covered with 

 thin epidermal plates which belong to the skin. The bony 

 nature of the carapace is 

 seen when the plates are 

 removed, or if its inner 

 surface is viewed (Fig. 

 267). It is seen to con- 

 sist largely of wide ribs 

 (how many ?) much flat- 

 tened and grown together 

 at their edges. The ribs 

 are seen to be rigidly at- 

 tached to the vertebrae. 

 The rear projections of 

 the vertebrae are flattened 

 into a series of bony plates 

 which take the place of 

 the sharp ridge found 

 along the backs of most 



vertebrates. 



Fig. 267. — Skeleton of European 

 Tortoise. 



C, rib plates; M, marginal plates: B, plastron; 

 //, humerus bone; R, radius; U, ulna; 

 Fe, femur. 



Fig. 268. — Three-cham- 

 bered Heart of a Rep- 

 tile (tortoise). 



a, veins; b,f, right and left auri- 

 cles; eg, ventricle; d, arteries to 

 lungs; e, veins from lungs; /',>/, 

 two branches of aorta. Compare 



with Fig. 269 and coloured Fig.2. 



Show that the shell 

 of a turtle is not homologous with 

 the shells of mollusks. Does the 

 turtle have shoulder blades and 

 collarbones? Hipbones? Thigh 

 bones ? Shin bone (fibia) and splint 

 bone (fibula) ? (Fig. 267.) 



Do the plates formed by the ribs 

 extend to the edge of the cara- 

 pace ? See Fig. 267. About how 

 many bony plates form the cara- 

 pace ? The plastron ? Do the 

 horny plates outside correspond 

 to the bony plates of the shell ? 



