634 COLLEGE ZOOLOGY 



and separate genital and anal apertures. The mouth is bounded 

 by soft, fleshy lips which aid in seizing and holding food. At 

 the end of the snout are two obvious slits, the nostrils. The 

 large eyes, one on either side of the head, are protected by an 

 upper and a lower eyelid bordered by thin eyelashes, and a white, 

 hairless third eyelid, or nictitating membrane, which may be 

 drawn over the eyeball, from the anterior angle. Above and 

 below the eyes and on either side of the snout are long, sensitive 

 hairs, the whiskers or vibrissa. 



The trunk may be separated into an anterior portion, the tho- 

 rax, which is supported laterally by the ribs, and a posterior 

 portion, the abdomen. The tail is short. Beneath it is the anus, 

 and just in front of this is the urinogenital aperture. On either 

 side of the anus and just anterior to it is a hairless depression, 

 the perineal pouch into which a strong-smelling secretion is 

 poured by the perinseal glands. Four or five pairs of small 

 papillae, the teats or mamma, are situated in pairs on the ventral 

 surface of the thorax and abdomen. At the end of the teats 

 open the ducts of the mammary or milk glands. 



The fore limbs of the rabbit are used, as in the frog, for holding 

 up the anterior part of the body. They possess five clawed digits 

 each. The hind limbs are longer and more powerful than the 

 fore limbs and serve as leaping organs. They are provided with 

 only four digits; the one corresponding to the great toe in man 

 is absent. The rabbit places the sole of its foot upon the ground, 

 and is, therefore, said to be plantigrade (L. planta, the sole of the 

 foot; gradior, walk). 



The Skeleton. — An outline of the skeleton is shown in Fig. 

 510. It consists principally of bone, but a small amount of 

 cartilage is also present. As in the fishes, amphibians, reptiles, 

 and birds, there are cartilage-bones, preformed in cartilage, and 

 membrane-bones, arising by the ossification of dermal portions 

 of the skin. A third type, called sesamoid bones, occurs in the 

 tendons of some of the limb-muscles, the action of which they 

 modify; for example, the knee-cap. 



