MUSCLE AND NERVE 39 



Annotation. Since the contracting muscle does not interchange material with 

 the medium, but merely shifts its substance, its volume is not altered. The men- 

 iscus remains stationary, provided all the air has been driven out of the saline by 

 boiling. 



8. Manner of Attachment of the Muscles to the Bones. Determine 

 the position of the fulcrum, weight and power in the cases of the biceps 

 in flexing the forearm, triceps in extending the forearm, muscles upon the 

 ventral aspect of the neck in moving the head, gastrocnemius in raising 

 the body on tiptoe, tibialis anticus in raising the body on the heel, and 

 the masseter in raising the jaw (Fig. 17). 



9. Center of Gravity. With chalk outline the feet of a person when 

 standing erect. Approximately determine by means of a ruler, held 

 vertical, the position of his center of gravity. Attach a heavy load first 

 to the front and then to the back of his body, and note the manner and 

 degree in which the body is shifted to support the center of gravity. 

 What use may be made of the legs and arms in gaining additional sup- 

 port? Draw a diagram illustrating the progression of the center of 

 gravity during the act of walking. 



