CEREBELLUM, PONS, AND MEDULLA. 225 



ture of the body is concerned, it is homolateral, that is, each half 

 of the cerebellum is connected with its own half of the body. 

 The connection with the motor areas of the brain is the re- 

 verse, the right half of the cerebrum being in relation with 

 the left half of the cerebellum. These relations are in the main 

 borne out by the anatomical course of the motor and sensory paths 

 described above. But those who have operated upon the cere- 

 bellum by the method of ablation agree entirely in the statement 

 that by this method at least no evidence is obtained of a localization 

 of function in the cerebellar hemispheres. There is no reason to 

 believe that extirpation of definite areas in the hemispheres affect 

 definite groups of muscles either on the sensory or the motor side. 

 We are forced to conclude, therefore, that localization is absent 

 and that regarding the cerebellum we must believe, as was formerly 

 believed regarding the cerebrum, that each half is everywhere func- 

 tionally equivalent. The effect of ablations is dependent not upon 

 the part removed, but rather upon the quantity. It is to be doubted, 

 perhaps, whether this view will stand the test of more complete 

 investigations, for some data exist that suggest the possibility of 

 .a localization. It is observed, for instance, that the effects of 

 ablation upon the movements of the animal are more marked the 

 closer the injury is to the mid-line,* that is, the more the vermi- 

 form lobe is involved. The possibility of a more or less definite 

 localization is suggested also by the effects of stimulation of the 

 cerebellar cortex. Ferrier especially has described definite move- 

 ments of the eyes, head, or limbs following electrical excitation of 

 definite regions of the cortex; but this indication has not been 

 developed by later experimenters with sufficient success to lead 

 to positive conclusions. 



The Medulla Oblongata. In the medulla oblongata we must 

 recognize a region of special physiological importance in that it 

 is the seat of certain centers which control the activity of the 

 -circulatory and respiratory organs. If the medulla is severed 

 from the portion of the brain lying anterior to it the animal con- 

 tinues to live for a considerable period. The respiratory move- 

 ments are performed rhythmically, and the blood-vessels retain 

 their tone so as to maintain an approximately normal blood-pressure. 

 On the contrary, destruction of the medulla, or severance of its 

 connections with the underlying parts, is followed by a cessation 

 of respiration and a loss of tone in the arteries, either of which 

 results in the rapid death of the organism as a whole. The portions 

 of the medulla which exercise these important functions are desig- 

 nated, respectively, as the respiratory and the vasomotor or vaso- 

 constrictor centers. Their location and to some extent their con- 



* Lewandowsky, loc. cit. 

 15 



