HUMAN STRUCTURE AND LIFE-ACTIVITIES 519 



the membranous wall of the inner ear. Through this mem- 

 brane vibrations are passed on to the fluid of the inner ear, 

 and its vibrations 

 stimulate the sen- 

 sory endings of the 

 auditory nerve 

 which are sensi- 

 tive to sound. 

 The semicircular 

 canals give us the 

 sense of equilib- 

 rium, of which we 

 are aware even 

 when we are blind- 

 folded. 



444. Smell, 

 Taste, Touch, 

 Temperature. 

 These senses are 

 connected with 

 special nerves. 



Those of smell have endings in the epithelium which lines cer- 

 tain upper cavities of the nose. The nerves of taste end in the 

 little projections (papillae) on the tongue. Those of touch and 

 temperature are widely distributed in the skin of all parts of 

 the body. 



THE SKIN AND ITS WORK 



445. Human Skin. Microscopic preparations show that 

 the surface of the skin is made up of closely set cells, while the 

 lower side next to the muscles and bones is made up of con- 

 nective tissue (Fig. 166). The cellular layer is the epidermis, 

 and the connective tissue is the dermis. 



(D) A piece of leather tanned without the hair will give a good 

 view of the intricately interlaced fibers of the dermis, the epidermis 



FIG. 165. Diagram of human ear. a, canal from 

 external ear ; t, tympanum ; m, middle ear 

 with small bones extending from tympanum to 

 inner ear ; s, one of the semicircular canals of 

 hmer ear ; c, cochlea of inner ear ; n, auditory 

 nerve ; 6, bone surrounding middle and inner 

 ears ; e, Eustachian tube, and p, its opening to 

 pharynx. 



