166 



SUBKINGDOM VERTEBRATA. 



Fig. 277. 



consolidated into an upper shell called the Carapace, while 

 the broadened sternum forms a lower one termed the Plas- 

 tron.* Into this portable cas- 

 tle the reptile retreats with 

 marvelous rapidity, f in one 

 genus the limbs and head be- 

 ing withdrawn so as to show 

 no apparent opening. The 

 viscera, the shoulder and hip- 

 bones, and the muscles are all 

 packed in the thorax. Breath- 

 ing is performed by enlarging 

 the cavity of the mouth, when 

 the air rushes in through the 

 nostrils, and by contraction is forced down the windpipe. 



Skeleton of a Marine Turtle. 



Cistudo virginiana, Box Tortoise. 



Chelydra serpentina, River Tortoise. 

 Chelys matamata, llcavded Tortoise. 



Snapping Tortoise. 



Chelonia midas, G. em Turtle. 



Testudinidae. The Land Tortoises J have feet formed 

 only for walking, and hence they never enter the water. 

 Their food consists of soft plants, as mushrooms. The plas- 

 tron of the female is convex, and that of the male concave. 



* The same number of pieces is found in the skeleton as in the ordinary verte- 

 bra t,es, the shape and size alone being changed. 



t The long, slender muscles which move the flexible neck are tied to the under 

 side of the carapace. When dried they may be capable of producing musical sounds 

 and thus have given rise to the poetical legend of the origin of the lyre. 



$ Many authors use the terms tortoise and turtle synonymously ; but the former 

 term is properly applied to the land species, and the latter to the marine. 



The " Gopher," a small tortoise about eighteen inches long, found at the South, 

 belongs to this family. It will burrow six feet in the ground. 



