74 University of California PuUications in Anatomy [^^o^. 2 



were also interrupted; and it was these fibers especially for which 

 such a decussation was claimed. If there should exist a bilateral 

 cortical somato-sensory representation of certain portions of the body 

 (regions near the median line), an assumption otherwise not very 

 probable, a partial re-crossing of the afferent somato-sensory tracts 

 must be achieved at levels below the thalamus or in the thalamus itself 

 (see Wallenberg). At any rate, the ''sparing" of the sensibility of 

 such peripheral regions of the body in cases of hemianaesthesia cannot 

 be explained by a re-crossing of a portion of the thalamo-cortical 

 radiation ; it is due rather to a sheltered position of portions of the 

 thalamo-cortical radiation in question and of the corresponding 

 cortical representations. (Compare the explanation of the preservation 

 of "central" or macular vision, Visual System.) 



4. BOUNDARIES OP THE SOMATO-SENSOEY PROJECTION CORTEX 



Apparently the most important result in the present investiga- 

 tions is that concerning the extent or boundaries of the somato-sensory 

 cortex (shaded areas on both sides of the sulcus centralis C and around 

 the sulcus cinguli Sc in fig. 6.) A careful tracing of the degenerated 

 thalamic fibers up to their cortical terminations showed that unques- 

 tionably the somato-sensory cortex does not merely occupy a narrow 

 strip, perhaps corresponding only with Brodmann's areas 1, 2, and 3, 

 stretching immediately behind and buried in the sulcus centralis (fig. 

 7), as accepted by almost all authorities at the present time. In fact, 

 the somatic sensory cortex occupies the entire precentral agranular 

 region and a considerable portion of the parietal granular region, in 

 addition to the entire postcentral granular region. In particular, the 

 somatic sensory cortex extends over Brodmann's areas 1, 2, 3, 4, 5, 6, 

 43, and the oral portion of area 7. In view of the long continued dis- 

 pute on the real functional significance of the precentral region, 

 especially of the so-called motor region or the area praecentralis gigan- 

 topyramidalis, area 4 of Brodmann, particular attention was paid to 

 the afferent fibers of that area. There cannot be, however, any doubt 

 that both areas 4 and 6 of Brodmann receive numerous afferent fibers, 

 which were traced from their thalamic origin up to and into the pre- 

 central cortex. However, certain differences exist as to the numerical 

 distribution of somato-sensory fibers to various cytoarchitectural areas 

 of the extensive pre- and postcentral somato-sensory cortex. There 

 are also features different and peculiar to each area, besides other 



