WHITE MATTER OF MEDULLA. 299 



and cortex. Between the cerebellum and the medulla it comprises 

 the acustico-cerebellar tract and, possibly, the cerebello-olivary 

 tract; and, therefore, is almost completely relayed in the vestib- 

 ular nuclei, the nuclei of the reticular formation, and, possibly, 

 in the inferior olivary nucleus (Figs. 94 and 95). It forms part 

 of the brachium pontis and restiform body through which it reaches 

 the medulla. In the lateral area, it descends along the anterior 

 lateral sulcus, to the corresponding area of the cord. It ends 

 (?) in the anterior columna of gray matter. It was once regarded 

 as a part of the anterior pyramidal tract. The anterior descending 

 cerebello- spinal tract forms a segment of the indirect motor path, 

 and the motor arm of the reflex arc of coordination and equil- 

 ibrium. 



Anterior Ascending Cerebello-spinal and Spino-thalamic 

 Tract. (Fasciculus ascendens cerebello-spinalis anterior) (Figs. 

 92 and 95). These two tracts are combined into one throughout 

 the cord, medulla and pons. Near the isthmus the former turns 

 backward through the superior medullary velum and ends in the 

 cortex of the superior vermis cerebelli; while the spino-thalamic 

 tract continues in the original direction, to the lateral nucleus 

 of the thalamus. The common spino-encephalic tract made 

 up of these two bundles takes its origin from the base of the 

 anterior columna and center of the crescent of gray matter, chiefly 

 on the opposite side of the spinal cord; and, crossing through 

 the white anterior commissure, it ascends, mingled somewhat 

 with the fibers of the above descending cerebello-spinal tract, 

 along the lateral surface of the cord (Barker). It runs beneath 

 the posterior lateral groove of the medulla and through the 

 formatio reticularis of the pons, to the point of division near 

 the isthmus rhombencephali, whence the two divisions proceed 

 to their cerebellar and thalamic terminations, as above stated. 

 The tract is probably reinforced in the medulla and pons by the 

 addition of axones from the opposite terminal nuclei of common 

 sensory cerebral nerves; and, rising primarily in relation with the 

 posterior roots of spinal nerves, it thus forms a crossed path for 

 common sensations, spinal and cerebral. It conducts tactile, 

 pain and temperature impulses (see pages 161 and 356). 



