46 University of California PuUications in Anatomy \.^''(>^- 2 



mately perpendicular to the long axis of the hemisphere and of the 

 thalamus. This probably means a subdivision of the investigated 

 fiber system according to certain qualities of somatic sensations. On 

 the other hand, every one of the fiber sheets in its turn has to be 

 imagined as being composed of individual bundles, each of which 

 enters a segment of a particular cyto-architectural area corresponding 

 with a special "center" according to the segmental representation of 

 the peripheral parts of the body. In other words, just as there is a 

 definite "spatial" arrangement in the efferent systems of the cere- 

 bral cortex, as for example in the pyramidal system where each of its 

 bundles arise from a definite small sector of the precentral "motor" 

 area, so there is a similar organization within the somato-sensory 

 afferent system with this notable qualification : that there are several 

 parallel afferent somato-sensory systems which seem to correspond 

 with the various qualities of the sensation conducted. A somatotopic 

 or a "spatial" organization of the afferent somato-sensory system 

 stands parallel in organization to the visual afferent system: similar 

 requirements of function have produced similar anatomical conse- 

 quences. (Compare Chapter XIX.) 



The present experiment gives additional proof that the pre- 

 central "motor" area is at the same time a receptive-sensory region. 

 Further it was found, as in the preceding experiments, that no 

 afferent somato-sensory fibers enter the corpus callosum to reach 

 the opposite hemisphere. The somato-sensory radiation is unilateral 

 from its origin in the thalamus to its termination in the cortex. 



The afferent fibers appear to be numerous everywhere in the cortex 

 of the delimited region, possibly even more abundant in the floor of 

 the central sulcus ; and the total as well as the relative number of affer- 

 ent fibers within the precentral "motor" cortex is quite considerable. 

 As in preceding experiments, the intracortical afferent fibers show 

 the same characteristics and the same differences between the pre- 

 central and the postcentral regions to be described in Chapter VII. 

 In the postcentral cortex their course is somewhat oblique, while in 

 the precentral cortex their course is more direct and perpendicular, 

 going for long distances in approximately the same direction. 



Finally, by the lesion of the internal capsule and of the lentiform 

 nucleus, a considerable number of efferent fibers which descend into 

 the pes pedunculi were interrupted. 



