WHITE MATTER OF THE SPINAL CORD. 



1045 



opposite sides, with contributions, possibly, from the cells of the intermediate gray 

 matter. After traversing the cord, the lateral field of the medulla, and the tegmental 



Fig. 899. 



Section of spinal cord at level of lower part of 

 fifth lumbar segment ; gray matter relatively large 

 in amount ; anterior cornua bulky. Preparation by 

 Professor Spiller. X 6. 



portion of the pons, the tract ascends the 

 brain stem to the vicinity of the inferior cor- 

 pora quadrigemina. Here the major part of 

 the fibres turn backward and, by way of the 

 superior cerebellar peduncle and the superior 

 medullary velum, reach the cerebellum to 

 end mostly in the superior worm, partly on 

 the same side and partly crossed (Hoche). 

 Possibly a part of the cerebellar contingent Ik^- ^^ 

 may share the path of the direct cerebellar •- >' '^ 

 tract and in this way reach the cerebellum 

 by its inferior peduncle (Ziehen). It is 

 possible that all fibres from Gowers' tract do 

 not pass to the cerebellum, but that some 

 continue upward to terminate in relation with 

 the neurones of the superior corpora quadri- 

 gemina and of the optic thalamus. The 

 fibres of the tract acquire the medullary 

 coat about the beginning of the eighth month of foetal life (Bechterew). 



The lateral ground-bundle (fasciculus lateralis proprius) of Flechsig includes 

 the remainder of the lateral column. Much uncertainty prevails as to its detailed 

 paths, but beyond question the composition of the ground-bundle is very complex 

 and comprises a number of long exogenous paths that descend from the brain, as w^ell 

 as one long ascending and many shorter endogenous strands, both ascending and 

 descending. These short tracts occupy chiefly the central parts of the lateral column 

 and, in a general way, lie close to the gray matter, within an area between the ante- 

 rior and posterior horns, known as the boundary zone. They are, however, not 

 limited to this field, as not a few of their fibres lie scattered among the longer 

 exogenous tracts occupying the more lateral portions of the ground-bundle. 



One long endogenous path, the spino-thalamic tract, is of unusual importance since it estab- 

 lishes a direct sensory link between the cord and higher centres. This tract arises from the 

 cells of the posterior horn of the opposite side, the axones crossing in the anterior commissure 

 to pursue a course brainward within the antero-lateral ground-bundle. Although the fibres of 

 this tract are scattered and not collected into a compact strand, their chief location is just medial 

 to Gowers' tract. Associated with the fibres destined for the optic thalamus are others {tradtcs 

 spiiio-tectalis) that end in the region of the corpora quadrigemina. 



The short endogenous tracts include both ascending and descending fibres which arise as 

 the axones chiefly of the marginal and inner cells of the posterior horn, some coming from the 



opposite side by way of the posterior intracentral commissure. 

 Entering the lateral column the axones undergo T-like division 

 with ascending and descending limbs. The former pass upward 

 for a distance that usually includes only from one to three 

 segments, then bend inward and enter the gray matter to end 

 probably in relation with other posterior horn cells. The down- 

 wardly directed limbs form the descending endogenous fibres, 

 which, in addition to occupying the boundary zone are also 

 scattered among the longer tracts of the ground-bundle. After 

 a relatively long course, they enter the gray matter to end 

 probably in relation with the anterior horn cells. They are, 

 therefore, regarded as establishing reflex-paths. Since these 

 endogenous strands link together various levels of the cord, they 

 are often collectively termed intersegmental association fibres. 

 The exogenous tracts of the lateral ground-bundle are closely 

 related with those found in the ground-bundle of the anterior 

 column and what may be said of the former largely applies to 

 the latter. Notwithstanding the study that these tracts have 

 received, much uncertainty exists as to their exact origin and termination ; it may be stated in 

 a general way, however, that they bring the higher sensory and coordinating centres into 

 relation with the spinal cord and constitute, therefore, descending paths other than the 



Secitou of spinal cord at level 

 of third sacral segment ; posterior 

 cornua with substantia gelatinosii 

 are relatively bulky. Preparation 

 by Professor Spiller. X 8. 



