36 University of California PuUications in Anatomy ["^"ol. 2 



situated bundles. Where thalamo-cortieal fibers form dense bundles 

 or systems, especially if their course is an oblique one ascending ventro- 

 dorsally and longitudinally, they might in normal preparations be 

 mistaken for short or even for long association bundles connecting 

 the frontal and occipital regions (figs. 50-53). 



The present experiment, compared with the foregoing one, exhibits 

 in a lesser degree, but none the less, the same arrangement of indi- 

 vidual bundles comprising thalamo-cortieal radiation, indicating a 

 functional segregation. The most dorsal fibers, arising from the dorso- 

 lateral thalamic nucleus directed toward the dorsal segments of both 

 central convolutions maintain an internal position. Others, orig- 

 inating in the ventro-lateral nucleus, and perhaps also, from the 

 hypothalamus, hold a lateral course along and through the putamen 

 and along the claustriim (fig. 51) ; their destination is the opercular 

 (ventral) segments of both central convolutions. Concerning these 

 ventro-lateral bundles, the statement made regarding the medial 

 (internal) bundles of the radiation can he repeated. The ventro- 

 lateral bundles, also, remain well removed from the convex aspect of 

 the hemisphere and have a good chance to escape destruction by a 

 pathological process provided the latter does not directly involve the 

 opercular cortex or the Sylvian fossa. In the extreme caudal and 

 most oral sections of the present series, many short sectors of fibers 

 are seen, indicating an oblique ascending course in both oral and 

 caudal longitudinal directions (respectively). 



An exact comparison of the thalamic fibers entering the precentral 

 and postcentral convolutions, respectively, is not easily made. Yet, 

 superficial examination is alone sufficient to establish the conviction 

 that the number of afferent fibers attaining the precentral gyrus is 

 scarcely below that reaching the postcentral gyms. Since, however, 

 the floor of the sulcus centralis and the adjacent narrow strip of pre- 

 central gyrus coating the anterior wall of the sulcus belong struc- 

 turally to the postcentral region (compare Chapters VI and VII), a 

 part of the dense bundles terminating in the floor of the sulcus 

 centralis, C in figures 46-48, reaches a cortical area which is a part 

 of the postcentral region. But, even so, there can be no doubt that, 

 numerically, many thalanio-cortical fibers definitely reach the pre- 

 central region (figs. 44-46). Their number per square unit appears 

 to be somewhat below that of the postcentral region, forming looser 

 bundles than those in the postcentral convolution. (In fig. 45, degen- 

 eration of a thin bundle of cortico-f ugal fibers was produced by a small 



