64 TISSUES OF A LIMB. 



made up of several parts, each performing an im- 

 portant office or function. Beneath this, proceeding 

 from without inwards another tissue comes into view, 

 very different from the first, called fat, or as it is 

 termed more correctly, adipose tissue. Beneath this, 

 again, is a firm, unyielding, glistening material, 

 spread out like a membrane, admirably adapted for 

 the protection of the more delicate structures beneath, 

 This is composed of a form of white fibrous tissue. 

 which is called Fascia. Next to this we come to a 

 peculiar tissue, which alternately becomes shortened 

 and lengthened according as it is influenced by 

 nerves. The change is said to depend upon the 

 property of contractility. Ordinarily, the tissue in 

 question is spoken of as flesh, but we call it muscle. 

 In connection with this, we invariably notice certain 

 cords which are the nerves. Their office is to bring 

 the muscular substance into relation with the brain and 

 other parts of the nervous system, and to convey to it 

 from the nerve centre those various impulses by which 

 not only its contraction and relaxation is effected, 

 but by which the exact degree of contraction willed 

 is established. Besides the tissue described, we 

 observe in various parts of the limb certain tubes, 

 which are of two kinds the one, with thick, tough, 

 and very elastic walls ; and the other, with walls less 

 elastic, thinner, and flaccid. Both sets of tubes are 

 in connection with the heart, but the one set (arteries) 

 performs the office of conveying the blood from the 

 heart to the tissues ; the other (veins), that of re- 

 turning the blood from the tissues to the heart, 

 40, 46. Besides these, there are some very delicate 

 tubes which are called lymphatics, which transmit 

 a colourless fluid from the tissues to the venous 

 circulation. Lymphatics cannot be seen without 

 being filled with some coloured substance. Lastly, 

 we notice the bone, a firm, hard, solid tissue, in the 

 interior of which is a cavity containing that peculiar 



