CEREBKO-SPINAL CONNECTIONS. 653 



interior white fibres proceed. Stilling describes in the front part of the middle lobe roof-nuclei 

 so called because they lie in the roof of the 4th ventricle. As is shown in fig. 462, the white 

 fibres of the superior peduncle pass to the grey matter on the inferior surface of the cerebellum, 

 while the inferior peduncular fibres pass to the superior surface, chiefly of the median part ; 

 but both are said to form connections with the corpus dentatum ; the middle peduncle is con- 

 nected with the grey matter of the lateral lobes. The minute structure is described in 380.] 



The distribution of the blood-vessels of the brain is of much practical importance. The 

 middle cerebral artery of the Sylvian fissure supplies the motor areas of the brain in animals ; 

 in man, the paracentral lobule is supplied by the anterior cerebral artery (Buret). The region 

 of the third left frontal convolution, which is the speech-centre, is supplied by a special branch 

 of the middle cerebral. According to Ferrier, that part of the brain, any injury to which 

 causes disturbance of intelligence, is supplied by the anterior cerebral; while those regions, 

 where injury is followed by hemi-ansesthesia, are supplied by the posterior cerebral. It is stated 

 that anaemia of isolated parts of this area of the brain is associated with melancholia in man. 



Conduction to and from cere Drum Voluntary motor fibres. The course 

 of the fibres which convey impulses for voluntary motion the pyramidal tracts 

 proceeds from the motor regions of the cerebrum ( 375, 378, I.), passing 

 into and through the white matter of the cerebrum through the corona radiata, 

 and converges to the internal capsule, which lies between the nucleus 

 caudatus and opticus thalamus internally and the lenticular nucleus externally 

 (fig. 500). [The motor fibres for the face and tongue occupy the knee of the 

 capsule (F), those for the arm the anterior third of the posterior segment or limb 

 (A), and those for the leg the middle third (L). They pass beneath the optic 

 thalamus, enter the crusta of the cerebral peduncle, and occupy its middle third, or 

 two-fifths, extending almost to the substantia nigra, the fibres for the face being 

 next the middle line, and those for the leg most external, the fibres for the arm 

 lying between the two. They pass into the pons on the same side, where the fibres 

 for the face (and tongue) cross to the opposite side, to become connected with the 

 nuclei from which the facial and hypoglossal nerves arise. The fibres for the arm, 

 and leg (and trunk) continue their course to the medulla oblongata, where they 

 form the anterior pyramids. In the pons, the pyramidal tracts are broken up into 

 bundles lying between its superficial and deep transverse fibres, and surrounded by 

 grey matter (fig. 503); but they have no connection with the grey matter of the pons. 

 By far the greater proportion of the fibres cross at the decussation of the pyramids 

 to form the crossed pyramidal tracts, or lateral pyramidal tracts, of the lateral 

 column of the opposite side. The small uncrossed portion is continued as the 

 direct pyramidal tract on the same side. The latter fibres, perhaps, supply 

 those muscles of the trunk (e.g., respiratory, abdominal, and perineal), which always 

 act together on both sides. According to other observers, however, they cross to 

 the other side of the cord through the anterior white commissure, and descend in 

 the crossed pyramidal tract or pyramidal tract of the lateral column. The fibres of 

 the pyramidal tracts split up into fine fibrils, which form connections with the 

 fibrils produced by the subdivision of the processes of the multipolar nerve-cells. 

 Thus, fibres form connections with the multipolar ganglionic cells of the anterior 

 cornu of the grey matter of the spinal cord at successively lower levels, and from 

 each multipolar cell is directed peripherally a single unbranched process, which 

 ultimately becomes a nerve-fibre. The pyramidal tracts thus end in the multipolar 

 nerve-cells of the grey matter of the spinal cord, from which the anterior roots of 

 the spinal nerves arise. 



[The course of the pyramidal tracts and the decussation of these fibres in the 

 medulla oblongata, explain why a haemorrhage involving the cerebral motor centres, 

 or affecting these fibres in any part of their course above the decussation, results in 

 paralysis of the muscles supplied by the fibres so involved on the opposite side of 

 the body. In their passage through the brain, the paths for direct motor impulses 

 are not interrupted anywhere in their course by ganglion cells, not even in the 

 corpus striatum or pons. They pass in a direct uninterrupted line, until each fibre 



