4 6 



Scientific Proceedings (51). 



33 (729) 



The motor cortex and pyramid tract in the raccoon 

 (Procyon lotor Linn.). 



By Sutherland Simpson. 



[From the Physiological Laboratory, Medical College, Cornell 

 University, Ithaca, N. Y.] 



The raccoon is a very intelligent animal and, as one would 

 expect, relatively to the size of its body, it possesses a large brain 

 with a highly convoluted cerebral cortex. Little appears to be 

 known, however, about its cortical topography or the fiber tracts 

 of its central nervous system. 



The present note refers to the experimental localization of the 

 motor areas and the subsequent tracing of the pyramid tract by 

 the method of ablation and secondary degeneration. Five full- 

 grown specimens were obtained. The cerebral cortex was exposed 

 on the left side, under ether anesthesia, the motor areas were 

 localized both by the bipolar and unipolar methods and then 

 removed. The wound was closed and the animal allowed to live 

 for about two weeks when the left hemisphere was exposed and 

 explored in the same way before the animal was finally dispatched 

 by an overdose of ether. The brain and spinal cord were removed 

 and treated by the Marchi method. 



The region from which muscular responses were obtained is 

 relatively large and well defined. It occupies the whole free 

 surface of what may be termed the post-cruciate convolution, 

 extending from the mesial border of the hemisphere to a little 

 way beyond the lateral extremity of the cruciate sulcus. Unless 

 when the current was comparatively strong, no movements were 

 obtained from the cortex in front of the cruciate sulcus. From 

 the mesial border lateralwards the order of the responsive areas 

 was as follows: anus, tail, hind limb and digits, body, fore-limb 

 and digits, head and eyes, and face, mouth and tongue, the last 

 curving forwards around the lateral extremity of the sulcus. The 

 movements were readily elicited and the areas well defined but 

 there was always some overlapping at the margins. The forearm 

 area appeared to be the most easily excited, that is to say, it 



