ADJUNCTS OF THE MUSCULAR SYSTEM. 101 



the forearm, its muscular fibres are very short, being placed 

 obliquely, and constituting a demi-penniform muscle, extend- 

 ing from the ulna to the tendon, which runs the whole length 

 of the forearm. 



Sometimes the sinewy intersections, which are placed 

 along the path of a muscle, have a special part to perform : 

 thus the intersections of the rectus of the abdomen divide 

 this muscle into as many distinct muscles, thus providing im- 

 partial contractions, which would be impossible in a long 

 muscle made entirely in one piece: the same may be said of 

 the numerous digastric muscles in the neck, and of the nape 

 of the neck (grand complexus, etc.). 



Mechanism of the jBones, considered as Severs. In the 

 play of the muscles, of the tendons, and of the bones we 

 find mechanical apparatus exactly similar to the three kinds 

 of levers. 



The lever of the first kind is to be often met with in the 

 animal economy. In the case of man we might call it the 



Fig. 27. Showing the equilibrium Fig. 28. Diagram of the foot and 

 of the head upon the vertebral ankle, the heel being raised by the 



column.* tendon of Achilles (Dalton). 



standing lever ; for it is in the equilibrium of the erect post- 

 ure that we find the greatest number of examples of it, and 

 it is very rare to find this kind used for movements of the 

 body. When the head is in equilibrium upon the vertebral 

 column, in the occipito-atloi dean joint (Fig. 27) it represents 

 a lever of the first kind, the point tfappui of which is its 

 junction with the vertebral column (in A). The resistance 

 (weight of the head) lies in the centre of gravity of the 



* Lever of the first class. A, Fixed point. R, Resistance (centre of. gravity 

 of the head). 1', I'orce (the arrows indicate the direction in which the force ami 

 the resistance act> 



