592 NERVOUS SYSTEM. 



posterior columns include either the white or the gray matter, they are called 

 respectively the anterior or posterior white and gray columns. Physiological 

 and pathological researches, however, have shown that the cord may prop- 

 erly be farther divided as follows : 



1. Columns of Tiirck. By the sides of the anterior median fissure, are 

 two narrow columns of white matter, one on either side, extending to the 

 white commissure (A, in Fig. 217), called the columns of Tiirck, the direct, 

 or the uncrossed pyramidal tracts. The fibres of these columns descend, 

 probably decussate in the cervical region of the cord, and the columns are 

 lost in the lower dorsal region. Destruction of certain motor parts in the 

 brain is followed by descending secondary degeneration of the fibres of these 

 columns. 



2. Crossed Pyramidal Tracts. These are situated, one on either side, in 

 the posterior portion of the lateral columns (G, G, in Fig. 217), and are 

 bounded internally by the posterior cornua of gray matter and externally by 

 a narrow band called the direct cerebellar tract. In following the columns 

 upward, it is found that they pass forward in the upper part of the cervical 

 region and decussate in the lower portion of the anterior pyramids of the 

 medulla oblongata. These are descending tracts, and their fibres undergo 

 descending secondary degeneration as the result of destruction of certain 

 motor parts in the brain. 



3. Anterior Fundamental Fasciculi. These fasciculi (B, in Fig. 217), 

 are bounded internally by the columns of Tiirck and externally by the ante- 

 rior cornua of gray matter and the anterior roots of the spinal nerves. Their 

 fibres are supposed to connect the gray matter of the anterior cornua of the 

 cord with the gray matter of the medulla oblongata. 



4. Anterior Radicular Zones. These columns (E, E, in Fig. 217) are in 

 the anterior portion of the lateral columns. Their fibres are supposed to 

 connect the gray matter of the cord with the gray matter of the medulla 

 oblongata. 



5. Mixed Lateral Columns. These columns (F, F, in Fig. 217) are in 

 the lateral columns of the cord, next the gray matter. With the anterior 

 fundamental fasciculi and the anterior radicular zones, they probably connect 

 the gray matter of the cord with the gray matter of the medulla oblongata. 



The fibres of the anterior fundamental fasciculi, the anterior radicular 

 zones and the mixed lateral columns do not degenerate in either direction as 

 the result of section of the cord. Their fibres seem to connect nerve-cells with 

 each other, and their trophic cells exist at both extremities, which accounts 

 for the absence of degeneration, just mentioned. 



6. Direct Cerebellar Fasciculi. These fasciculi (H, H, in Fig. 217) are 

 situated at the outer and posterior portion of the lateral columns. Their 

 fibres pass to the funiculi graciles, or posterior pyramids of the medulla 

 oblongata, and thence to the cerebellum, by the inferior peduncles. They 

 connect the cells of the posterior cornua of gray matter with the cerebellum. 

 These columns make their appearance first in the lumbar region of the cord, 

 and they increase in size from below upward. After section of the spinal 



