

STRUCTURE AND FUNCTIONS OF THE CEREBRUM 177 



now have positive proof of a high degree of specialization of func- 

 tion in the cortex. 



Sensory Areas. In previous paragraphs the paths of the 

 various senses were traced as far as their entrance into the cere- 

 brum by way of the internal capsule. We must now continue 

 the paths to their cortical terminations. The body sense fibers 

 pass to that part of the parietal lobe just behind the fissure of 

 Rolando; the region where they terminate is the body sense area. 

 The visual tracts end in the occipital lobes in the visual areas. 

 The auditory tracts terminate in the temporal lobes in a region 

 just below and within the fissure of Sylvius; this region constitutes 

 the auditory area. Although the paths of smell and taste are 

 imperfectly known, their cortical terminations have been fairly 

 well established. The olfactory area is supposed to be in the tem- 

 poral lobe, and possibly at its very tip. The area for taste, gusta- 

 tory area, is thought to be also in the temporal lobe, probably 

 adjacent to the area for smell. Since the nerve-paths of the 

 various senses lead directly to these areas, and since destruction 

 of any one of them, by accident or disease, results in loss of the 

 particular sense whose area is involved, we must conclude that the 

 sensory areas are the receiving stations of the cerebrum. All 

 afferent projection fibers entering the cerebrum terminate in one 

 or another of the sensory areas. Within these areas they have 

 synaptic connection with the association neurons of the region. 



The Motor Area and the Pyramidal Tracts. In each hem- 

 isphere a region of the frontal lobe just in front of the fissure of 

 Rolando contains numerous giant pyramidal cells whose axons 

 extend into the white matter and are grouped together in the 

 internal capsule as a conspicuous nerve tract, called the py- 

 ramidal tract. It extends through the midbrain to the medulla and 

 appears upon the ventral surface of the latter as a well-marked 

 anatomical feature. About midway of the medulla the pyramidal 

 tracts cross the mid-line in the decussation of the pyramids (K. fig. 

 66). This decussation is not complete; part of the fibers of each 

 pyramidal tract continue along the same side of the medulla to 

 the spinal cord and down the latter in the ventral column, forming 

 the direct pyramidal tract. That part of each pyramidal tract 

 which crosses over at the " decussation " proceeds along the spinal 

 cord in the lateral column as the crossed pyramidal tract (Fig. 65). 



