228 STUDENTS HISTOLOGY 



the horns of gray matter. They are united just in front of the 

 anterior gray commissure by white matter the white commissure. 

 The spinal nerves take origin from the gray cornua, the anterior 

 roots from the anterior, and the posterior roots from the posterior 

 cornua. The white substance consists essentially of medullated 

 nerve -fibers which, with the exception of the anterior spinal 

 nerve -roots and the commissural fibers, pass mainly in a longi- 

 tudinal direction. 



The anterior,/ lateral, and posterior columns into which the 

 white matter isi primarily divided, may be divided secondarily 



FIG. 148. HUMAN SPINAL CORD FROM THE LUMBAR REGION. STAINED BY THE 

 WEIGERT-PAL METHOD. SLIGHTLY MAGNIFIED. PHOTOMICROGRAPH. 



into certain other columns or tracts which are indicated in Fig, 

 146. These tracts are often called by the name of the discoverer. 

 The principal ones are as follows : 



The direct pyramidal tract: Tiirck. 



The ascending antero -lateral tract: Gowers. 



The descending antero -lateral tract. 



The crossed pyramidal tract. 



The direct cerebellar tract. 



The postero- external tract funiculus cuneatus: Burdach. 



The postero -internal tract funiculus gracilis: Goll. 



The demonstration of the different tracts we owe partly to 

 pathology, since in certain diseases' definite tracts may be involved 

 throughout the length of the cord, while the others may be exempt. 

 The alterations which ensue in the diseased parts make it easy to 

 trace such tracts. 



