1932] Poliak: Afferent Fiber Systems, Primate Cerebral Cortex 55 



Chapter VII 



CORTICAL TERMINATIONS OF SOMATOSENSORY 

 AFFERENT FIBERS 



In the same uninterrupted series of the brains of Macaeus described 

 before and stained aeeording^ to Marehi's method, the minute relations 

 of the intracortical terminations of thalamic fibers were studied. 

 Experiment II proved to be especially valuable since the completeness 

 of degeneration of the thalamo-cortical radiation apparently reached 

 its maximum here. It was, therefore, assumed that the preparations 

 of cortex where compact fiber bundles enter show, in this series, a com- 

 plete picture of all the existing intracortical terminations of the 

 afferent somato-sensory fibers. The identity of degenerated intra- 

 cortical fibers in Experiments II, III, and V-a where the radiation 

 was interrupted outside the thalamus, and that of the actual thalamo- 

 cortical fibers was easily established by comparing them with Experi- 

 ment I, where no doubt could arise as to the thalamic origin of 

 similar fibers. 



The mode of termination of thalamic fibers within the somatic 

 sensory cortex so far, of course, as this could be determined by 

 Marehi's method, in particular the relation of fibers to special cell and 

 fiber layers of the cortex and other characteristic features such as the 

 size, course, and numeric distribution of fibers to various cytoarchi- 

 tectural areas given below, is a combined result drawn from all four 

 experiments. 



Thalamo-cortical fibers as said before (see Chapters V and VI) 

 reach an extensive territory of the hemisphere. Since, as mentioned 

 previously, afferent somato-sensory fibers are most dense around the 

 central sulcus (narrow, deeply shaded area in fig. 6 completely sub- 

 merged in the central furrow) their minute relations were most 

 conveniently studied here. 



Penetrating into the cortex of the bottom (fundus) of the central 

 sulcus, somato-sensory fibers invade in a great number the lower third 

 of the cortex near the subcortical white substance (figs. 9, 60 repre- 

 sent the dorsal extremity of the sulcus centralis showing a portion of 

 fig. 48 at a higher magnification ; in fig. 9 all details in the drawing, 

 except the outlines, represent degenerated fibers). Here numerous 



