38 THE SKIN. 



many othei* textures, and reaches the utmost confines 

 of the system. Its structure is elaborate, and its 

 work in some cases never ceases for a moment as 

 long- as hfe lasts. Unlike every other tissue in the 

 hody, the nervous tissue exhibits uninteiTupted con- 

 tinuity of texture. There is not a thread in any part 

 of the nervous system the tissue of which is not con- 

 nected with the nerve tissue of other parts, — which is 

 quite disjoined from other threads and nerve matter. 

 61. The muscular tissue is to be detected at a veiy 

 early period, and two different kinds of tissue having 

 conti'actile property can be distinguished in man and 

 the higher animals. The movements of one being 

 under control of the will, through the interven- 

 tion of nerve tissue is termed voluntary muscle, the 

 other, although equally under nervous control, is not 

 directly influenced by the will, and indeed contracts 

 without our being conscious. This is called organic 

 or involuntary muscle. Such a division is, however, 

 not strictly accurate, and it is better to speak of these 

 two kinds of muscular tissue respectively as the striped 

 or transversely sfriafed muscle and the tmsiriped 

 muscle. Although examples of the first are usually 

 under voluntary control, and therefore propei-ly termed 

 voluntary muscle, instances are not wanting of striped 

 or transversely striated muscle which is not under 

 the influence of the will. At an early period of de- 

 velopment the striped muscle resembles the non- 

 striated in general appearances as will be described 

 when muscular tissue comes under consideration. 



62. The skin.— As would be supposed, a texture 

 composed of so many difierent tissues as the skin 

 and performing so many important functions, acquires 

 its perfect development but slowly. Connected with 

 the cutaneous system ai'e nails, hairs, and in many of 

 the lower animals horny structures. The glands for 

 the secretion of the sweat open upon the surface of the 

 skin, and the sebaceous glands secreting oily matter 



