192 



FIRST LESSONS IN ZOOLOGY. 



four limbs, and follow another path leading to the turtles. 

 And in these creatures we have very singular, highly-modi- 

 fied forms, specially adapted to a life of unusual security. 

 Nature has been kind to the turtles; she has given them a 

 strong shell, into which the head and legs may be with- 

 drawn, so that they can get all the food they want, and yet 

 not become food for other animals. She has endowed them 

 with wonderful vitality and long life, adapting them for 

 life on the land, in rivers and lakes, and in the high seas. 

 If the turtle is slow, it is sure; it does not push itself along 



M 



FIG. 199. Skeleton of the common Spotted Turtle. Mn, mandible; O, orbit of 

 eye; A, ear-opening; //, hyoid bone; Cer, cervical vertebrae; Dor, dorsal ver- 

 tebrae consolidated with the carapace, (Jura; Can, caudal vertebrae; .S, 

 scapula; Co, coracoid; St. sternum: Hum, humerus; K<id, radius; Ul, ulna; 

 Cur, carpal bones' M, metacarpals; //, ilium; Pub, pubic bone; Is, ischium; 

 Fein, femur; J', tibia; F, fibula; Tin; tarsus; Pes, foot. 



on its belly, like an ordinary lizard, but its legs are so per- 

 fectly formed that it can walk, lifting its body above the 

 ground ; its senses are acute, so that it can perceive coming 

 danger and withdraw into its shell, or, if near or in the 

 water, dive to the bottom out of harm's way. 



No one is at a loss to recognize a turtle at sight; all have 

 a shell, and the toothless jaws are protected, as in birds, by 

 horny sheaths. 



The skeleton of the turtle should be carefully examined. 

 It will be seen that the shell consists of an upper bony shield 

 and a lower shield, which is joined to the upper by lateral 

 arches; the upper shell, or carapace, then, is partly due to 



