THE MUSCLES. 



105 



Fig. 43. 



t\ 



ml 



60. When a muscle contracts, it swells ; its fibres, 

 which in a state of repose, were straight, fold in zig- 

 zag, (Figs. 41, a/,d 42.) and their two extremities are 

 brought n n ar to each other, drawing also with them 

 the parts to which they are attached, but their volume 

 is not augmented. 



61. The two extremities of muscles are 

 solidly fixed to the bones, and to the other 

 parts which they are designed to set in 



motion, such as the skin, through the medium of white 

 cords, called tendons, (Fiy. 43.) or membranes of the 

 same nature, named a/xmcuroses, or fascia. In con- 

 tracting, they must necessarily draw towards each other 

 the two bones to which the tendons or aponeuroses are 

 attached. An example will enable us better to under- 

 stand this mechanism. 



If we suppose the muscle, m. (Fiy. 44.) 

 to be attached to the humerus, and to 

 the ulna or cubitus, which articulates 

 first, forming the elbow joint, by 

 moveable ligaments, it is evident 

 that when this muscle contracts, 

 these bones will approach each 

 other, as is seen in Fig. 45. This 

 example will give an idea of all 

 the motions of the skeleton. 



62. The number of muscles of the human body is very con- 

 siderable ; they are reckoned at 470 ; in general, they form about 

 the skeleton two layers, and are distinguished into superficial 

 and deep seated 



63. The muscles which are designed to move any particulai 

 bone, are almost always placed around that portion of the skele- 



Fig. 44. 



Expla nation of Fig. 41. A fragment of muscle showing- the muscular 

 fasciculi (bundles of muscular fibres,) straight, and at u-st. 



Explanation of Fig. 42. The same in a state of contraction. 



Explanation of Fig. 43. A muscle (m.) with the tendons (<,/.) by which 

 it is attached to the bonrs. 



Explanation of Fig. 44. Bon? of the arm (h.) and the fore-arm, (af.) 

 with one of the flexor muscles of ihe fore-arm (m.) \\\ a state of rest. 



Explanation of Fig. 45. The same at the moment of contraction. 



60. What changes lake place by the contraction of a muscle? 



61. To wh it prLs are the extremities of the mu<clt s attached ? What is 

 .he necessary consequence of ihe contraction of a muscle ? 



62. What is the disposition of the muscles? How are they distinguished .' 



63. How are the muscles, situate^ 

 move ? 



to the parts they are destined 



