354 SPECIAL PHYSIOLOGY. 



THE SENSE OF TOUCH. 



The Organ of Touch. 



The skin is the principal part of the body concerned in the sense of 

 touch, but the tongue and lips also possess this sense. The nails and 

 hairs are appendages of the skin, and often minister to the sense of 

 touch. The skin is further provided with sebaceous and sudoriferous 



f lands. It constitutes a protecting covering to the whole body, and is 

 nown as the common integument. 



The skin consists of an external or superficial layer, destitute of 

 bloodvessels and nerves, named the cuticle, Fig. 66, 1, 2 ; and of an 

 internal or deeper layer, abundantly supplied with nerves, and highly 

 vascular, known as the cutis vera or true skin, 3. These two layers, 

 though separable, are closely adherent. 



The skin is thicker on the back than on the front of the body, 

 thicker on the outer than on the inner surface of the limbs, thicker 

 still in the palms of the hands but thickest of all in the soles of the 

 feet. It is very thin on the eyelids, in the tube of the ear, and on the 

 red borders of the lips, where it becomes continuous with the mucous 

 membrane of the mouth. The surface of the skin is marked with fine 

 intersecting lines or furrows, which divide it into minute angular 

 spaces ; these are large opposite the foldings of the 

 Fig. 65. joints. On the soles and palms, and especially on 



the toes and fingers, the skin is elevated into little 

 ridges, usually parallel to one another, which sweep 

 over the surface in curved lines, Fig. 65 ; they cor- 

 respond with rows of the vascular eminences be- 

 longing to the true skin, named the papillae. 



The cuticle, also called the epidermis (ere, upon, 

 and dsp/ia, the skin), is made up of superimposed layers 

 of nucleated epidermoid cells. (See p. 65, Fig. 43.) 

 The superficial cells, Figs. 66, 67, 1, are flattened, 

 dry, and transparent, and firmly held together, as- 

 suming at the surface, the form of thin, coherent, 

 horny scales ; the cells in the deeper layers, 2, 2, 

 resting on the cutis, are soft, roundish, or corn- 

 Fig. 65. Portion of the pressed, and easily separated from each other ; this 

 !^ ii th hti end uia 'n? ^ ee P er layer is known as the rete mucosum of Mal- 

 ned, showing the curved pighi, or, sometimes, as the Malpighian layer, or the 

 ridges and intermediate mucous layer. The color of the skin in the dark 



ducts of the sweat glands, in the form of colored granules, usually situated in 

 certain of the epidermoid cells. These granules are 

 fewer near the surface of the cuticle, where the flattened scales are 

 paler. The color of the skin is, therefore, chiefly seated in the rete 

 mucosum of the cuticle ; the true skin, in the dark races of men, has 

 the same color as that of the European. 



It is the non-vascular cuticle which, owing to the exudation of a 



