630 HANDBOOK OF PHYSIOLOGY. 



fibres which proceed to the spinal cord, and are there represented as 

 the pyramidal tracts. 



This is the reason, no doubt, that movements are produced on stimu- 

 lation of the white matter after the superficial gray matter of the 

 animal's brain has been sliced off. 



Motor tracts in the brain. These motor fibres are connected with the 

 pyramidal cells of the cortex, and are indeed their continuations. 



It will be necessar} 7 , therefore, to trace them from the cortex down- 

 ward. From the motor area of the cortex they converge to the inter - 



Fig. 383. Diagram to show the connecting of the Frontal Occipital Lobes with the Cere- 

 bellum, etc. The dotted lines passing in the crusta (TOC), outside the motor fibres, indicate the 

 connection between the temporo-occipital lobe and the cerebellum. F. c. , the fronto-cerebellar 

 fibres, which pass internally to the motor tract in the crusta; I.F., fibres from the caudate 

 nucleus to the pons. FR., frontal lobe; Oc. , occipital lobe; AF., ascending frontal; AP., ascend- 

 ing parietal convolutions ; PCF. , precentral fissure in front of the ascending frontal convolution ; 

 PR. , fissure of Rolando ; TPF. , interparietal fissure, a section of cms is lettered on the left side. 

 SN. , substantia nigra ; PY. , pyramidal motor fibre, which on the right is shown as continuous 

 lines converging to pass through the posterior limb of ic. internal capsule (the knee or elbow 

 of which is shown thus *) upward into the hemisphere and downward through the pons to cross 

 at the medulla in the anterior pyramids. (Gowers.) 



nal capsules^ and pass down to the crusta of the crus in the way already 

 indicated. 



In the internal capsule the fibres which pass onward and downward 

 to the pyramidal tracts of the spinal cord do not occupy more than a 

 small section, namely, that part known as the knee, and the anterior 

 two-thirds of the posterior segment (fig. 384). In this district the 

 fibres for the face, arm, and leg, are in this relation : those for the face 

 and tongue are just at the knee, and below or behind them come first 

 the fibres for the arm and then those for the leg. 



The more accurate arrangement of these fibres in the monkey's brain 

 from above down are those for the eye, head, tongue, mouth, shoulder, 



