194 



STUDIES IN PHYSIOLOGY 



of them are directed by the conscious portions of our brain. 

 Thus we can close our fingers and open them as we please ; 

 we can move the eyes, the head, and the legs at will. We 

 call all the muscles that are controlled by our will power, 

 vol'un-ta-ry muscles (Latin voluntas = will). Most of the 

 muscles of the throat, those of the gullet, stomach, and 

 intestines, on the other hand, act without any voluntary 

 direction on our part, and they are therefore called in-voV- 

 un-ta-ry. 



1. THE VOLUNTARY MUSCLES * 



The Biceps Muscle. When I place my left hand on the 

 front surface of my right upper arm, and then draw up my 



right forearm as 

 far as possible, I 

 feel the muscle 

 in front of the 

 humerus become 

 shorter, thicker, 

 and harder. By 

 extending the 

 forearm again, a 

 tough cord or 

 ten 1 don can be 

 felt at the lower 

 or distal end of 

 the muscle. This 

 tendon attaches 

 the muscle to the 

 radius bone. The proximal end of this muscle is covered by 

 thick layers of flesh, but if these were removed, we should 

 find two other tendons, which connect the muscle with pro- 

 jections on the shoulder blade (Fig. 88). We are now pre- 

 pared for certain definitions. The muscle we have been 

 studying is called the bi'ceps, from the fact that its upper 



iSee "Laboratory Exercises," No. 33. 



FIG. 88. Action of the Biceps Muscle. 



a = attachment of tendons to shoulder. 

 _?* = elbow point. 



P = attachment of lower tendon to the radius. 

 W = weight of the hand. 



