no 



THE NERVOUS SYSTEM 



same side of the cord. They form a tract of small size, which lies near the 

 anterior median fissure and which can be traced as a distinct strand as far as the 

 middle of the thoracic region of the spinal cord. Just before terminating these 

 fibers cross in the anterior white commissure. They end like those of the lateral 

 corticospinal tract, either directly or perhaps through an intercalated neuron, 

 in relation to the motor cells in the anterior column. The crossing of these 

 fibers is only delayed, and it will be apparent that all of the corticospinal fibers 

 arising in the right cerebral hemisphere terminate in the anterior column of the 

 left side of the cord, and conversely, those from the left hemisphere end on the 

 right side. It is along these fibers that impulses from the motor portion of the 

 cerebral cortex reach the cord and bring the spinal motor apparatus under 

 voluntary control. 



Fasciculus septomarginalis 



Fasciculus inlerfascicularis 



Fasciculus proprius 



Sensory fibers of the 

 second order ~ 

 Lateral corticospinal _ 

 tract 



Rubrospinal tract I- 

 Tectospinal tract - - 

 Fasciculus proprius NT 



Bulbospinal tract 



Vestibules pinal tract--, 



Fasciculus gracilis 



.,-- Fasciculus cuneatus 



- - - Dorsolateral fasciculus 



^_ Dorsal spinocerebellar 

 tract 



~~ Fasciculus proprius 



Ventral spinocere- 

 bellar tract 

 jf-.. Lateral s pinotltalamic 



tract 

 Spinotectal tract 



- Ventral root 



~~ Ventral spinolhalamic tract 



* T . " Sulcomareinal fasciculus 



Ventral cortjcosptnal tract 



Fig. 78. Diagram showing the location of the principal fiber tracts in the spinal cord of man. 

 Ascending tracts on the right side, descending tracts on the left. 



It is stated by some authors, although on the basis of rather unsatisfactory evidence, 

 that the fibers of the lateral corticospinal tract ramify in the formatio reticularis (Mona- 

 kow, 1895) and the nucleus dorsalis (Schafer, 1899). The corticospinal path is from the 

 standpoint of phylogenesis a relatively new system and varies a great deal in different 

 mammals. It is found in the ventral funiculus in the mole, while in the rat it occupies the 

 posterior funiculus. In the mole it is almost completely unmyelinated, in the rat largely so. 

 It contains many unmyelinated fibers in the cat, fewer in the monkey (Linowiecki, 1914). 

 In man it does not become fully myelinated before the second year. An uncrossed ventral 

 corticospinal tract seems to be present only in man and the anthropoid apes, and this tract 

 varies greatly in size in different individuals. 



The rubrospinal tract (tract of Monakow) is situated near the center of the 

 lateral funiculus just ventral to the lateral corticospinal tract (Fig. 78). Its 

 fibers come from the red nucleus of the mesencephalon, cross the median plane, 



