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HANDBOOK OF PHYSIOLOGY. 



in words, has been associated with disease of the posterior part of the 

 lower or third frontal convolution on the left side. This condition is 

 usually associated with paralysis of the right side (right hemiplegia). 



This district of the brain is now generally known as the motor area; 

 and there seems no doubt whatever that from this area pass the nerve- 

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

 pyramidal tracts. 



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

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

 mal'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 necessary, therefore, to trace them from the cortex down- 



FIG. 359. 



FIG. 360. 



Fro. 359. Diagram to show the connecting of the Frontal Occipital Lobes with the Cerebellum, 

 etc. The dotted lines passing in the crusta (TOG), 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., ascending parietal convolutions; 

 PCF., pre-central fissure in front of the ascending frontal convolution ; FR., fissure of Rolando; 

 IFF., inter-parietal 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 *) 

 upwards into the hemisphere and downwards through the pons to cross at the medulla in the 

 anterior pyramids. (Gowers.) 



FIG. 360. Diagram to show the relative positions of the several motor tracts in then' course 

 from the cortex to the crus. The section through the convolutions 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.) 



wards. From the motor area of the cortex they converge to the internal 

 capsule, a comparatively narrow band of fibres passing first of all be- 

 tween the two parts of the corpus striatum, namely, the intra-ventric.u- 

 lar portion, or caudate nucleus, and the extra-ventricular portion, or 

 lenticular nucleus, and then between the optic thalamus internally and 



