ANATOiMY AND PHYSIOLOGY 27 



medulla, cerebellum, and optic lobes, (5) in the diencephalon and 

 cerebral hemispheres, and (6j in the muscles. In addition, on the 

 basis of your observations and reading, state (7) the function of the 

 entire central nervous system and (8) the function of the nervous 

 system as a whole. 



(i) When, in the course of the demonstrations mentioned in the 

 preceding paragraph, did the frog die? Write a brief statement justi- 

 fying your answer and explaining the meaning of life and death. 



H. The Muscular System 



Exercise 22. — The Muscles. 



(a) Remove the skin from an uninjured hind leg. The flesh is now 

 seen to be made up of a considerable number of muscles which may be 

 readily separated from each other. These muscles fall into two 

 classes: the flexors, which bend a joint, and the extensors, which 

 straighten it. Each muscle has a thickened middle portion and tapers 

 toward the ends. Muscles are attached to bones by tendons which are 

 continuous with the connective tissue sheath that surrounds and helps 

 to bind together the numerous muscle cells that make up each muscle. 



(bj Study the gastrocnemius muscle, the large muscle in the calf 

 of the leg. To what bones is it attached? The large tendon at its 

 posterior end is the tendon of Achilles. Compare this with the same 

 tendon in man and other animals. Determine the relation of this 

 muscle to movements- of knee and ankle by moving the joints. Does 

 it serve as flexor or as extensor for these joints? Look on the front 

 of the leg for muscles which oppose the action of the gastrocnemius 

 in the ankle region. Observe the two sets of muscles in the thigh. To 

 what bones are they attached? What muscles are brought into play 

 when the frog suddenly straightens the leg, as in jumping or swim- 

 ming? Remove the muscles of the thigh, noticing their attachments 

 and their mechanical possibilities. ]Make a diagrammatic drawing 

 (X 2) showing the relation of the gastrocnemius muscle to the bones 

 of the leg. Indicate, in the diagram or in writing, the motions pro- 

 duced by its contraction, 



I. The Skeletal System 



Exercise 23. — The Skeleton. 



(a) Study mounted skeletons. Identify the major parts and learn 

 the names of the chief bones by reference to the list given here. 

 Compare the skeleton of the frog with that of man and any other 

 forms that are available. How do the several parts correspond and 



