ANIMAL BIOLOGY. [Part I. 



region are guarded with ribs, which meet the sternum or 

 breast-bone below. The walls of the abdominal region are 

 soft. 



The whole skin is invested with an exoskeleton consisting of 

 hairs, greyish brown on the back and limbs, white on the belly 

 and under the tail. On the general surface of the body the 

 hairs are of two kinds ; larger and longer contour hairs (pili), 

 and shorter and softer fur (tana or lanugo). In the seal at the 

 Zoological Gardens we see the hair ; but in the dressed sealskin 

 the hair is removed, and we see only the prepared and dyed 

 fur. Special hairs are developed on the face : the vibrissce or 

 mystaces on the upperl ip ; the supra-orbital hairs, answering to our 

 eyebrows ; the eyelashes, and the malar vibrissce or cheek whiskers. 

 These vibrissse may be regarded as long and delicate sense- 

 levers. The hair is reflected into the mouth, so as to line the 

 inner side of the cheeks, and is continued over the under 

 surface of both fore and hind feet. 



If a few hairs be mounted in glycerine, and examined under 

 the microscope (low and high power), each will be seen to have 

 three layers : (1) a delicate external layer or cuticle, composed of 

 slightly overlapping scales, best seen near the tip of the hair; 



(2) beneath this a longitudinally fibrous layer, the cortex ; and 



(3) a central layer of irregular structure, the medulla (Fig. 30, 

 vi. vii.). 



There are nine external apertures, three median and three 

 pairs lateral. The anterior median aperture is the mouth, 

 bounded by upper and lower lips, the former having a groove 

 which passes upwards to the external nares. In front of the 

 mouth are the large gnawing or incisor teeth ; further back and 

 separated from these by a long space or diastema are the grind- 

 ing teeth (premolars and molars). In a very young rabbit there 

 are three incisors on each side of the mid-line in the upper jaw, 

 one larger and two smaller, one of the latter being just behind 

 the larger tooth. In the lower jaw there is only one incisor on 

 each side. There are three grinding teeth on each side in the 

 upper jaw, and two in the lower. In the adult rabbit there are 

 only two incisors in the upper jaw, the little ones to the side 



