506 ZOOLOGY. 
nine in number. The jaws are toothless, being, as in birds, 
encased in horny beaks*; there are rarely fleshy lips; the 
tongue is spoon-shaped and immovable. The heart consists 
of two auricles and a ventricle. The brain has larger cere- 
bral lobes than in the lizards. - The eyes have a third lid, or 
nictitating membrane. The student can best obtain an 
idea of the organization of the turtles by studying the skel- 
eton and dissecting a turtle with the aid of the accompany- 
ing description and figure of the common turtle. 
The common swamp-turtle (Chrysemys picta) is a good 
type of the Chelonia. The animal is enclosed in a hard shell 
made up of an arched dorsal portion, and a flat ventral por- 
as 
Ry Car, 
‘Mum, Go. ise, Pub. OY. 
Fig. 445.—Skeleton of the common spotted turtle. Mn, mandible; 0, orbit of 
eye; A, ear-opening; H, hyoid bone; Cer, cervical vertebrae; Dor, dorsal verte- 
bree consolidated with the carapace (Cara); Cau, caudal vertebrae; S, scapula; 
Go, coracoid; St, sternum; Hum, humerus; Rad, radius; Ul, ulna; Car, carpal 
bones; M, metacarpals; Ii, ilium; Pub, pubic bone; Js, ischium; Fem, femur; T, 
tibia; F, fibula; Tar, tarsus; Pes, foot. 
tion, the two connected laterally, but widely separated an- 
teriorly to give exit to the head and fore limbs, and pos- 
teriorly for the tail and hind limbs. These parts can all be 
withdrawn within the protecting shell, by being doubled or 
folded back upon themselves. The soft parts of the skin are 
covered with scales, formed by overlapping folds. The limbs 
are stout; upon the anterior feet there are five, upon the 
posterior four claws. On the under surface of the short 
tapering tail near its base is the wide opening of the cloaca. 
The ventral plastron consists of twelve symmetrical pieces, 
six on each side, Fig. 445. The first and last pair are tri- 
angular, the others are four-sided; the fourth pair is the 
* Tecth occur in the embryo of Trionyx (Wiedersheim). 
