ANATOMY AND PHYSIOLOGY 



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After the olfactory nerves are cut the entire central nervous system 

 can be placed in a watch glass and studied under water from the 

 dorsal, ventral, and lateral aspects. Make any necessary corrections 

 of your drawing. Identify again the third and fourth ventricles. 

 Cut away the dorsal surface of the cerebral hemispheres and find 

 the first and second ventricles, or lateral ventricles as they are called. 

 The narrow canal connecting the third and fourth ventricles will 

 probably not be seen. The fourth ventricle is continuous with the 

 central canal which runs the length of the spinal cord. The cavity 

 of the central nervous system contains the cerebrospinal fluid. It 

 should be recalled that one of the distinguishing characteristics of the 

 Phylum Chordata, of which the frog is a member, is the presence of a 

 tubular central nervous system which is dorsal in position. 



Exercise 21. — Localization of Functions in the Sensory-neuro- 

 muscular System. 



(h) It is possible to obtain some information concerning the local- 

 ization of functions in the sensory-neuro-muscular system by succes- 

 sive observations on frogs from which parts of the nervous system 

 have been removed. The reactions of a normal frog and of frogs in 

 which the following parts of the nervous system have been destroyed 

 will be demonstrated: (1) the cerebral hemispheres and diencephalon ; 

 (2) the entire brain; and (3) the entire central nervous system. In 

 the frog in which the entire central nervous system has been destroyed, 

 watch what happens when the sciatic nerve is cut, pinched, or other- 

 wise stimulated. What happens when an electric current or other 

 stimulus is applied directly to the gastrocnemius muscle? Observe a 

 frog's heart which has been removed from the animal and placed in 

 warm 0.7% salt (sodium chloride) or Ringer's solution. Your obser- 

 vations should be recorded in a table such as the one shown in Fig. 23. 



Localization of Functions in the Sensory-neuro-muscular System 



Fig. 23. — Form of table for record of Exercise 21. 



