THE FUNCTIONS OF THE CEREBRAL CORTEX 



283 



designated on the figure. The electrically excitable motor cor- 

 tex is of two types, marked on the figure by stipple and vertical 

 cross-hatching respectively. Stimulation of the latter areas in 

 the frontal and occipital lobes calls forth conjugate movements 

 of the eyes, and the physiological characteristics of these areas 

 are very different from those of the areas in the precentral gyrus, 

 which are shaded with stipple. This gyrus is the true motor 

 projection center, and a comparison of Figs. 132 and 133 with 

 Fig. 130 shows that its limits coincide tolerable closely with 



Fig. 133. The human cerebral hemisphere seen from the left side, upon 

 which the functional areas of the cortex are indicated. The area marked 

 "motor speech" is Broca's convolution. (From Starr's Nervous Diseases.) 



area 4 of Brodmann's chart of the anatomically distinct cortical 

 areas, including, however, a part of the cortex farther forward 

 in area 6. 



The structure of the cortex in the precentral motor area 

 (Brodmann's area 4) is very characteristic. In this region the 

 fifth layer of the cortex (see Fig. 127) contains a type of large 

 pyramidal cells (giant pyramids or Betz cells) which are found 

 nowhere else in the brain. From these cells arise most of the 

 fibers of the pramidal tract (tractus cortico-spinalis). This 



