MAMMALIA. 317 



and, in many other respects, a tendency to a child-like 

 conformation. 



PIG. 83. HEAD OF A -FEMALE. 



The body is everywhere covered by a common integument 

 called the skin, beneath which is a layer of areolar and 

 adipose tissue, which last has its cells filled with fat, which 

 during life is in a liquid or oily state ; this serves to protect 

 the parts beneath both from cold and violence, fills up the 

 hollows and irregularities between the muscles, and gives 

 the body a more rounded and graceful appearance. 



Man, in common with all the higher animals, is possessed 

 of the five " special senses," namely, sight, smell, hearing, 

 touch, and taste, the organs of which are the eyes, nose, ears, 

 skin, and mouth ; but these are developed in very different 

 degrees in different animals. 



Sight is the sense by which we take cognisance of those 

 external objects which either give out or reflect light. The 

 eye (fig. 84) is an optical instrument of great beauty and per- 

 fection, and by its help an image of everything we look at is 

 produced in miniature on the expanded optic nerve called the 

 " retina," as an image is produced in the " camera," which 

 instrument is made in imitation of the eye ; this image by 

 some unknown power is perceived by the mind, and produces 



