VIIL] THE MUSCLES. 281 



LESSON VIII. 



THE MUSCLES. 



1. The MUSCLES of man are his "flesh," and it is the 

 muscles of cattle which are eaten as " the lean " of " meat." 



These muscles are fleshy masses of different sizes and 

 shapes, separated from each other by membranes termed 

 aponenroses. Aponeuroses are included amongst those 

 fibrous and soft parts of the skeleton (referred to in Lesson 

 II.) which extend outwards from the bones of the endo- 

 skeleton to the skin, or exo-skeleton. 



The nature of muscular tissue has already been sufficiently 

 described in the " Elementary Physiology," Lesson XII. 

 15 ; the action of muscles in Lesson VII. 4 ; their fixed 

 points, 5 and 6; the kinds of movement they give rise 

 to, 17; and their modes of attachment in 19. 



2. That end of a muscle which is nearest to the central 

 axis of the whole body, or to the root, or else to the axis of 

 the limb of which it forms part, is generally called its ORIGIN, 

 and its proximal end. The opposite extremity is generally 

 called its INSERTION, and its distal end. 



Muscles are very often inserted into bones by means of 

 tendons, and then frequently, when such muscles are strong, 

 part of the bone extends out, as it were, a little way into the 

 substance of the tendons. Hence arise many such tuberosi- 

 ties, spinous processes, &c., as we have already made ac- 

 quaintance with. All the processes of the backbone are so 

 connected with tendons of muscles. 



3. Muscles acting on bony levers produce definite MO- 

 TIONS, in consequence of which certain epithets are applied 

 to such muscles. 



Thus, when two bones are united by a hinge-joint, muscles 

 which by their contraction tend to make the angle formed by 



