270 AN INTRODUCTION TO ZOOLOGY 



The underside of the tail and adjacent perineal regions of the body 

 are quite white. Altogether it is very inconspicuous against almost 

 any background in the light of the early morning or evening, when 

 it comes out to feed. It passes most of its time in a burrow in the 

 ground, and a number live close together, each pair with their own 

 hole, forming a community termed a warren. 



The front end of the head is drawn out into a blunt snout. The 

 mouth is not large, but noteworthy in that the upper lip is cleft 

 vertically in the middle line, a feature that enables the animal to 

 employ its teeth for gnawing without this lip getting in the way. 

 Above the mouth are the openings of the two external nares. The 

 upper lips bear a series of long stout hairs, the vibrissse, whose roots 

 have the endings of certain nerves specially related to them, and so 

 constitute a sensory apparatus of considerable use to the animal 

 for feeling its way in its dark underground home. The eyes are 

 large, but not prominent, and provided with well-developed upper 

 and lower lids. At their inner corner, or canthus, is the nictitating 

 membrane, which is capable of being drawn partly across the eye. 

 External ears, or pinnae, are strongly marked and well provided with 

 muscles ; in some domestic varieties they do not stand upright as 

 in the wild form, but droop down over the sides of the head, producing 

 a variety known as a lop-eared rabbit. 



The perineum is marked by bearing white fur. On it open the 

 alimentary canal by the anus and the urogenital ducts, and it also 

 has a pair of small perineal pouches and two small bare areas on 

 which open the ducts of the perineal glands to the secretion of which 

 the animal owes its characteristic odour. The rabbit, like all 

 mammals, is dioecious, and so the perineal areas of the two sexes 

 are different. The female urogenital aperture is a slit-like opening, 

 the vulva, bearing in its roof at the ventral end a rod-like structure, 

 the clitoris. The corresponding aperture in the male is borne at the 

 end of a conical rod-like projection, the penis, which is covered 

 by a fold of skin, the prepuce, so that at first sight the urogenital 

 apertures of the two sexes appear somewhat similar. On the 

 perineum of the male at each side of the base of the penis lies a small 

 scrotal sac, within which is contained the testis. It is characteristic 

 of most mammals that the testes leave their primitive position on the 

 dorsal side of the abdominal cavity, and pass into a single or paired 

 outgrowth of the peritoneal cavity which projects on the outside 

 of the body in the perineal region. The last of the external features 

 that call for notice are the mammary glands. These number four 

 or five pairs, situated on the lines joining the armpits, or axillae, and 

 the corresponding or inguinal regions of the leg. In the male, 

 although present, they are hard to distinguish ; in the female, 



