THE NERVOUS SYSTEM. 



631 



elbow, digits, abdomen, lip, knee, digits. These fibres come for the 

 most part from the part of the cortex on either side of the fissure of 

 Rolando, hence called the Rolandic area on either side. But the areas 



Fig. 384. Diagram to show the relative positions of the several motor tracts in their course- 

 from the cortex to the crus. The section through the convolution is vertical ; that through the 

 internal capsule, I, C, horizontal ; that through the crus again vertical. C, N. caudate nucleus 

 O, TH, optic thalamus; L2 and L3, middle and outer part of lenticular nucleus; /, a, I, face 

 arm, and leg fibres. The words in italic indicate corresponding cortical centres. (Gowers. ) 



for the head and eyes lie more anterior in the frontal lobe, to the front 

 of the precentral sulcus, that for the head above that for the eyes, and 

 an area for the trunk (not indicated in the fig. 383), is situated more 

 toward the middle line of the hemisphere, internal to that for the leg. 



But there are other fibres which are arranged in front of the 

 pyramidal fibres in the front limb of the capsule, as well as others behind 

 them in the hind limb of the capsule. Those in front are from the 

 anterior part of the frontal lobe, and these in passing into the crus are 

 found on the median side of the pyramidal fibres (fig. 383). They 

 appear to end in the gray matter of the pons, and there to be connected 

 with fibres from the middle peduncle of the opposite side of the cere- 

 bellum. Those behind the pyramidal fibres in the hind limb of the cap- 

 sule are from the temporal-occipital lobe. These fibres pass into the crus 

 to the outer side of the pyramidal fibres (fig. 383), they probably also 

 end in the gray matter in the same way. There are other fibres from the 

 corpus striatum, from both nuclei, but particularly from the caudate 

 nucleus, which pass to the crus, and are situated between the pyramidal 

 tract and the locus niger (fig. 383), some of which terminate in that 

 nucleus, while others terminate in the pons. Besides the above fibres, 

 all of which are believed to be efferent fibres, and are at any rate fibres 

 of descending degeneration, there are fibres which pass from the cortex 

 to the optic thalamus and tegmentum, fibres of ascending degeneration 



