53° 



COLLEGE ZOOLOGY 



another by cup and ball joints. The thoracic or trunk vertebrae 

 bear ribs which are closely united with the carapace. They lack 

 transverse and articulating processes. 



The pectoral and pelvic girdles (Fig. 439) are peculiarly situated 

 within instead of outside of the ribs. They serve, in fact, as 



A B 



N 



tax 



a»* 



(I.I! J 



Fig. 440. — Skull of a turtle, Trionyx gangelicus. A, dorsal; B, ventral aspect. 

 bo, basioccipital ; bsph, basisphenoid ; ch, internal nares; exo, exoccipital ; 

 fr, frontal; j, jugal; mx, maxilla; n, external nostril; op, opisthotic; pa, parietal; 

 pi, palatine; pmx, premaxilla; prf, prefrontal -f- nasal; pro, prootic; ptf, post- 

 frontal; q, quadrate; quj, quadratojugal; s, supratemporal fossa; so, supra- 

 occipital; sq, squamosal; vo, vomer. (From Zittel.) 



braces to keep the plastron and carapace apart. The limbs 

 are almost typically pentadactyl. 



The Digestive System. — Turtles feed on both plants and 

 animals; some are entirely vegetarian. The animals preyed 

 upon are water-fowl, small mammals, and many kinds of in- 

 vertebrates. The flexible neck enables the turtle to rest on 

 the bottom and reach out in all directions for food. The jaws 

 of the snapping-turtle, Chelydra serpentina, are powerful enough 

 to amputate a finger, or even, in large specimens, a hand. 



