126 



ELEMENTS OF PHYSIOLOGY 



no nerves and very few blood vessels. Some muscles 

 have a tendon at only one end ; some have no tendon but 

 are attached directly to bones. Find muscles without 

 tendons by studying the figures. The cordlike nature of 

 tendons can be ascertained by feeling the tendons under 

 the knees, called hamstrings, or the tendons in the angle 

 of the elbow. 



4 



FIG. 117. Tapping 

 Floor with Toe. 

 Lever of first order. 



FIG. 118. Raising 

 Weight of Body 

 upon Ankle. 



Lever of second order. 



FIG. 119. Raising 

 a Weight upon 

 Toes. 



Lever of third order. 



214. How Muscles and Bones Cooperate. When you 

 grasp a heavy weight in the hand and lift it by bending the 

 elbow, where is the muscle that does the work ? You will 

 easily find it in the upper arm ; this muscle is called the 

 biceps because it is attached to the shoulder blade above by 

 two tendons. The lower arm acts as a lever with the 

 fulcrum, or fixed point of the lever, at the elbow (Fig. 1 16). 

 It is easy to see that a slight contraction of the biceps 

 muscle will move the weight a greater distance than is 

 accounted for by the shortening caused by the actual con- 

 traction of the muscle. This is what the bones usually 

 accomplish for the muscles; they change a slow, short, 

 inadequate movement into a long, swift movement. While 

 the muscle contracts an inch, the bone may move a foot. 

 The bones thus add greatly to the range and rate of motion. 



215, Figures 117, 118, and 119 show the three orders of 

 levers. In the lever of the first order, the fulcrum (F) is 



