FIBER TRACTS OF THE SPINAL CORD 109 



and most conspicuous of these are the cerebrospinal fasciculi, which are more 

 properly called the corticospinal tracts. There are two in each lateral half of 

 the cord, the lateral and the ventral corticospinal tracts. Their constituent 

 fibers take origin from the large pyramidal cells of the precentral gyrus or motor 

 region of the cerebral cortex and pass through the subjacent levels of the brain 

 to reach the spinal cord (Fig. 77). Just before they enter the spinal cord they 

 undergo an incomplete decussation in the medulla oblongata, giving rise to a 

 ventral and a lateral corticospinal tract. 



The Lateral Corticospinal Tract (Crossed Pyramidal Tract, Fasciculus 

 Cerebrospinalis Lateralis). The majority of the pyramidal fibers, after cross- 

 ing the median plane in the decussation of the pyramids, enter the lateral fu- 



Cerebral hemisphere 



Spinal 

 cord 



Fig. 77. Diagram of the corticospinal tracts. 



niculus of the spinal cord as the lateral corticospinal tract, which occupies a posi- 

 tion between the dorsal spinocerebellar tract and the lateral fasciculus proprius 

 (Fig. 78). In the lumbar and sacral regions, below the origin ot the dorsal 

 spinocerebellar tract, the lateral corticospinal tract is more superficial. It can 

 be traced as a distinct strand as far as the fourth sacral segment; and as it 

 descends in the spinal cord it gradually decreases in size. Throughout its 

 course in the spinal cord it gives off collateral and terminal fibers which end in 

 the gray matter. 



The ventral corticospinal tract (fasciculus cerebrospinalis anterior or direct 

 pyramidal tract) is formed by the smaller part of the corticospinal fibers, which 

 do not cross in the medulla, but pass directly into the ventral funiculus of the 



