V 



^842 THE NERVE SYSTEM 



In the lateral column the following tracts may be enumerated: 

 Ascending : 



1. Dorsolateral spinocerebellar tract (Flechsig). 



2. Superficial ventrolateral spinocerebellar tract (Gowers), 



3. Spinothalamic tract. S /H*^ Wet* d*JL^* k+* ~f~ 7 



4. Spinomesencephalic tract) s fjMs^^/ <*~~+~a J*^-^* f {fo*' r *~ A ^"^ 

 Descending: 



1. Crossed pyramidal tract. 



2. Ilubrospinal tract. 



3. Cerebrospinal tract ( March i and Lowenthal). 



4. Lateral vestibulospinal tract. 



5. Olivospinal tract of Helweg. 

 Associating: 



1. Fasciculus lateralis proprius. 



The dorsolateral spinocerebellar or direct cerebellar tract (of Gratiolet and Flech- 

 sig) lies at the periphery, laterad of the crossed pyramidal tract. Its axones 

 >arise from the cells of Clarke's 4 column and ascend uninterruptedly to the medulla 

 oblongata. and thence to the vermis of the cerebellum in its inferior or post- 

 peduncle. The tract becomes more massive as the cord is ascended (Fig. 610). 



The superficial ventrolateral spinocerebellar tract, or tract of Gowers, also courses 

 along the periphery, but farther ventrad. The origin of its axones is yet in dis- 

 pute; they probably arise from cells in the gray substance of both sides, in the zone 

 between the dorsal and ventral horns as well as from some of the ventral horn 

 cells. The destination of the axones of this tract is equally uncertain, but most 

 of the fibres have been traced through the dorsolateral region of the medulla ob- 

 longata and the pontile reticula, whence it turns dorsimesad, to enter the cerebellum 

 through the superior medullary velum and ends in the dorsal vermis. A lesser 

 portion of the tract has been traced to the quadrigeminal bodies, while other groups 

 of axones end in various levels of the gray substance. 



The spinothalamic and Spinomesencephalic (tractus spinotectalis) tracts are 

 not gathered into compact bundles, but are rather scattered among the fibres of 

 the lateral column just mesad of the superficial ventrolateral spinocerebellar 

 tract (Gowers). The axones of both systems arise from cells in the dorsal horn 

 and its cervix of the opposite side, coursing through the white ventral commissure 

 and ascending the cord, the spinothalamic fibres ending in the thalamus, the 

 Spinomesencephalic fibres ending in the region of the quadrigeminal bodies. 

 The two tracts are collectively called tractus spinotectalis et thalamicus. 



The crossed pyramidal tract (lateral cerebrospinal fasciculus) occupies an ap- 

 proximately triangular or oval area in the dorsal portion of the lateral column, 

 just mesad of the direct cerebellar tract, except in the lumbar cord, where it lies 

 at the surface. The axones of this tract arise from the pyramidal cells of the 

 cerebral cortex (motor area") of the opposite side. After having descended^ 

 through the internal capsule, crusta. poris. to the pvramis of the medulla oblonp'ata , 

 the major portion (85 to 90 per cent.) of the fibres derived from one-half of the 

 brain decussate with those of the other half, crossing the median line to descend. 

 in the lateral column of the cord. The fibres which do not decussate constitute^ 



the direct pyramidal tract in the ventral coin mnV As the crossed pyramidal 

 tract descends it diminishes in size as its axones become distributed to the ventral 

 horn, where they terminate either in contiguity with the ventral motor cells which 

 give rise to the fibres of the ventral ( motor) nerve roots, or else in contiguity with 

 the dendrites of interposed neurones, which, in turn, convey the impulse to several 

 associated motor neurones presiding over the actions of associated muscles: 

 The bundle becomes exhausted as a distinct strand at the level of the fourth 

 sacral segment. 



