NERVOUS SYSTEM. 



CHAPTER XXIII. 

 THE FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM. 



The Effects of Bemoval of both Cerebral Hemispheres. In the 

 frog the cerebral hemispheres contain only a single layer of nerve- 

 cells and have reached only a very low stage of development. If the 

 cerebral hemispheres be destroyed by rapidly compressing the anterior 

 part of the skull between the blades of a pair of Spencer Wells' forceps 



FIG. 90. Diagram of the frog's FIG. 91. Diagram of a reflex 



brain. 1, Olfactory lobe; 2, arc, m = the motor nerve arising 



cerebrum ; 3, pineal gland ; 4, from a nerve-cell in the anterior 



thalamencephalon ; 5, optic lobe; horn of the spinal cord and end- 



6, cerebellum; 7, fourth ventricle ing by a motor end plate in a 



and medulla oblongata. muscle; s = the sensory nerve 



arising from a nerve-cell in the 

 posterior root ganglion and form- 

 ing a series of dendrites around 

 the motor nerve-cell above and 

 possessing a sensory nerve end- 

 ing in the skin below. 



there will be no loss of blood and the optic thalami will escape injury. 

 The first effect of the operation will be a general depression of the 

 nervous system, a condition known as shock. This will quickly pass 

 off and the brainless frog will show spontaneous movements, will swim 

 if placed in water, will turn over if placed upon its back, and will 

 behave generally as a normal frog. 



