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TEXT-BOOK OF PHYSIOLOGY. 



uterine life, the efferent fibers from it become myelinated during the third 

 month of extra-uterine life. 



By the same method of reasoning the gustatory, olfactory, auditory, and 

 visual sense areas are to be regarded as sensori-motor in character, for embryo- 

 logic investigations show that subsequently to the myelinization of the 

 afferent tracts connecting the sense-organs with the cortex, efferent nerve- 

 tracts arise from or near to the same centers and undergo myelinization. In 

 other words, these areas are primarily sensor and secondarily motor, and 

 therefore should be termed sensori-motor. In Flechsig's own terminology 

 each corticopetal or afferent tract is accompanied by a corticofugal or 

 efferent tract. 



CONCRETE CONCEPT 



FIG. 252. THE AREAS AND CENTERS OF THE LATERAL ASPECT OF THE HUMAN HEMICEREBRUM. 



(C. K. Mills.) 



In this view sensations, or the mental processes the outcome of sensations, 

 are the immediate cause of the movements of the muscles connected with both 

 the sense-organs and skeletal structures. Though this interpretation viz., 

 the coincidence of sensor and motor areas appears more in accordance 

 with the facts than the earlier view, it must be admitted that there are many 

 facts both of a physiologic and pathologic character which it is difficult to 

 harmonize with it. 



The Motor Area of the Chimpanzee Brain. In a series of experi- 

 ments made by Sherrington and Griinbaum on the brain of the chimpanzee 

 it was discovered that the so-called motor area was not so widely distributed 

 as in the monkeys generally, but was confined almost exclusively to the 

 convolution just in front of the fissure of Rolando, as it was impossible to 

 obtain any movement on direct stimulation of the convolution just behind it. 

 All points on the surface of the pre-central convolution, including the portion 

 forming the wall of the Rolandic fissure itself, were found to be excitable 

 and productive of movement when stimulated. The sequence of representa- 



