CEREBRAL LOCALIZATION 679 



involves the motor points of this particular part. The location of 

 the trephine opening may then be determined with almost mathe- 

 matical precision. 



Effects of the Ablation of the Motor Area. — In dogs, the destruc- 

 tion of one motor area results in an incomplete paralysis of the muscles 

 of the opposite side of the body. This condition is known as hemi- 

 plegia, the term biplegia being used when both sides are affected. 

 While this muscular disturbance usually attains its height within a few 

 hours after the injury, it gradually becomes less acute later on and 

 disappears in the course of a few days. During the interim, however, 

 the dog betrays a decided weakness of the muscles situated on the side 

 opposite to the injury, and generally walks upon the back of the paws. 

 Furthermore, those muscles which usually act together, never exhibit 

 so decided a degree of paralysis as those which are not directly related. 



Fig. 343. — Diagbam Illustkating the Disposition of the Motor and Sensory Points 

 IN THE Brain op the Dog (A) and the Brain or the Monkey (B). 

 In the former animal motor and sensory paralysis generally occur together, because 

 their points intermingle, while in the apes and man they do not. 



Consequently, the muscles of respiration and those of the trunk in gene- 

 ral are weakened but never paralyzed. This fact indicates that they 

 are innervated by both hemispheres. 



These motor disturbances are associated as a rule with a very 

 decided loss of the tactile sensations and the muscle sense. It ap- 

 pears, therefore, that the motor area of the dog, i.e., the anterior 

 and posterior central convolutions of each side, also embraces certain 

 sensory points, representing the end stations of the incoming fibers 

 pertaining to these sensations (Fig. 343). This intermingling of the 

 motor and sensory points, however, is not in evidence in the monkeys, 

 apes and man. It will be shown later on that in these animals the 

 former are concentrated more and more in the precentral and the latter 

 in the postcentral convolution, inclusive of the neighboring region of 

 the parietal lobe. Hence, it is possible to obtain in these animals 

 a motor paralysis which is not accompanied by disturbances of sen- 

 sation. Conversely, they may show sensory anesthesias without loss 

 of motion. 



