990 FIBRES OF THE PEDAL SYSTEM. [BOOK in. 



capsule, but occupy the fore limb (Fig. 122, fron). Thence they 

 pass to the crus, of which they form the small inner, median 

 portion of the pes (Fig. 114, Fr.), and from the crus pass into the 

 pons ; in transverse sections of the pons they are seen as scattered 

 bundles (Fig. 113, F.C.) to the median side of the pyramidal fibres. 

 But here they seem to end; the degeneration of the tract is a 

 descending one, and ceases here. Most probably the fibres end in 

 the nerve cells of the grey matter, which as we have seen is 

 abundant in the pons. It is also probable that through these 

 nerve cells the fibres of this tract are connected with transverse 

 fibres passing along the middle cerebellar peduncle into the cere- 

 bellum of the opposite side ; but this has not been definitely 

 proved. 



Posterior or temporo- occipital cortical. Fibres from. the grey 

 matter of parts of the cortex behind the motor area also converge 

 to the internal capsule, forming the hinder end of the hind limb 

 behind the pyramidal tract (Fig. 121, S). These fibres also con- 

 tribute to form the crus cerebri, passing into the pes, of which 

 they occupy the outer lateral portion (Fig. 114, Pr.O.). From the 

 crus they pass into the pons, where, like the fibres of the pre- 

 ceding tract, they appear to end, and probably in a like manner. 

 This fact has been described as one of ascending degeneration, 

 but in all probability like the preceding is one of descending 

 degeneration. 



The above three tracts of fibres may therefore all be regarded 

 as starting from or having their trophic centres in the cortical 

 grey matter of the hemispheres, as all helping to form, first the 

 internal capsule and then the pes of the crus cerebri. But while 

 the pyramidal tract passes, in part, to the spinal cord, the other 

 two cease at the pons, and probably through the grey matter of 

 the pons make connections with the cerebellum. Further while 

 the pyramidal tract coming from the middle region of the cortex 

 occupies a middle position in the capsule and a middle position 7 

 in the crus, the system from the front part of the cortex occupied 

 a front position in the capsule and an inner or median position 

 in the crus, and the system from the hind part of .the cortex a 

 hind position in the capsule and an outer or lateral position in 

 the crus. As the three systems pass from the cortex through the 

 capsule to form the pes of the crus, their positions in relation to 

 each other are shifted from one plane into another. As the fibres 

 spread out from the pes through the capsule to all parts of the 

 cortex, or, put in another way, as they converge from the cortex 

 through the capsule to the pes, they form a fan, the corona radiata, 

 which is not only curved, but the constituent parts of which cross 

 each other. 



Besides these three systems all passing from various regions of 

 the cortex to the crus, there is yet a fourth strand contributed to 

 the pes by the cerebral hemisphere though not starting in the 



