680 THE CEREBRUM 



In the monkey, the ablation of the motor area gives rise to very 

 marked and permanent symptoms. Very instructive observations 

 have been made by Goltz upon macacus whose left frontal and parietal 

 cortex had been removed by two operations. The animal remained 

 under observation for eleven years. The decided hemiplegia fol- 

 lowing directly after the operation, gave way in the course of two 

 months to a more moderate paralysis of the muscles of the right side. 

 This disturbance, however, persisted so that the animal always retained 

 a certain clumsiness of movement. It also showed certain sensory 

 defects for the obvious reason that the lesion also involved the post- 

 central and parietal gyri. In walking, climbing and jumping the muscles 

 of the left side were always relied upon most; in fact, unless made to 

 use the right hand, the animal preferred to employ the left hand. It 

 appears, therefore, that the motor area of the monkey is of much 

 greater functional importance than that of the dog for the reason 

 that it is concerned with those higher forms of movements which 

 can only be acquired by training and experience. Obviously, it is more 

 difficult to reestablish a center for skilled movements than it is to 

 compensate for the loss of a center controlling the less specialized 

 movements of the dog. This deduction is in complete harmony 

 with the greater specificity of the pyramidal system of the higher 

 animals as well as with the fact that the motor functions of the latter 

 have gradually been brought under the control of the cerebral hemi- 

 spheres. This is true especially of man in whom almost all muscular 

 actions are dominated by the cerebrum. It need scarcely be em- 

 phasized that this higher innervation necessitates experience and 

 education, two processes which are not essential to the lower forms, 

 because their actions are largely determined by subcortical centers. 

 For this reason we cannot be surprised at the helplessness of infants 

 as against young animals much lower in the scale of the Animal 

 Kingdom. 



In further analysis of this subject matter it may be inferred that the 

 recovery from lesions of the motor area must be least complete in 

 man. The histories of such cases show that this injury is invariably 

 followed by a contralateral paralysis, the extent of which is propor- 

 tionate to the size and severity of the central defect. Moreover, in 

 those cases in which the lesion remains confined to the anterior central 

 convolution, no true sensory disturbance arises. 1 It is also to be 

 observed that the paralysis involves chiefly those muscles which 

 are under the guidance of the will and are not paired in function. 

 In other words, the muscles of respiration, such as the diaphragm, 

 the abdominal and intercostals and those of the larynx, are excepted. 

 While a certain recovery from the immediate effects of the lesion may 

 take place in the course of time, hemiplegic muscles never regain their 

 normal usefulness. 



It has been mentioned above that hemiplegia is frequently asso- 



1 Monakow, Ergebn. der Physiol., 1902. 



