552 TEXT-BOOK OF PHYSIOLOGY 



peduncle enter and terminate as the name implies in the cerebellum. 

 A decussation of the fibers, it is stated, takes place in the superior 

 vermiform process. When transversely divided the peripheral por- 

 tion of the fibers undergoes degeneration. 



2. The Lateral Spino-cerebellar Tract, or Tract ofGower. This tract lies 

 on the ventral aspect of the lateral funiculus. It is composed of 

 fibers which also have their origin in nerve-cells of Clark's vesicular 

 column on the same side in the lower portion of the cord. From this 

 origin the fibers pass outward to the surface and then pass upward 

 as far as the pons Varolii where for the most part they turn backward 

 and enter the cerebellum by way of the superior peduncle. When 

 transversely divided the peripheral portion of the fibers undergoes 

 degeneration. 



3 The Lateral Spino-thalamic Tract. This tract lies just internal to the 

 lateral spino-cerebellar tract and has frequently been confounded with 

 it. It consists of fibers that have their origin in nerve-cells in the 

 dorsal horns of the opposite side. 



4. The Ventral Spino-thalamic Tract. This tract is located in the ventral 



fasciculus proprius just in front of the ventral horn of the gray matter. 

 The fibers composing this tract likewise have their origin in the nerve- 

 cells in the dorsal horn of the opposite side. 



From their origin the fibers of both these tracts cross to the opposite 

 side of the cord and pass upward in the regions just stated to terminate 

 around the cells of the lateral and ventral nuclei respectively of the 

 thalamus. These two spino-thalamic tracts are continued by third neur- 

 ons, which, arising in the cells of the thalamus, pass upward to the cells 

 of the post-central convolutions of the cortex of the cerebrum and are 

 known as the thalamo-cortical tracts. 



5. The Spino-tectal Tract. This tract lies ventral to the lateral spino- 



cerebellar tract. The fibers composing it arise in all probability from 

 cells in the gray matter of the opposite side of the cord. After cross- 

 ing the median plane they pass upward in the region just stated and 

 terminate around cells in the tectum or roof of the midbrain in the 

 region of the corpora quadrigemina. 



6. The Spino-olivary Tract. This tract, triangular in shape, lies near the 



surface of the ventral funiculus, somewhat ventral to the spino-tectal 

 tract. The fibers composing it are believed to have an origin similar 

 to [those of the foregoing tract. Superiorly they terminate around 

 cells in the inferior olivary nucleus in the medulla oblongata. The 

 last two tracts are frequently spoken of as the spino-mesencephalic 

 tracts. Collectively all these ascending tracts or fasciculi are spoken 

 of as the spinal lemniscus. 



The Descending Tracts or Fasciculi. The descending tracts, found in 

 the lateral and ventral funiculi, are four in number as follows: 

 i. The Cortico-spinal or Pyramidal Tract. l The fibers composing this tract 



1 From the fact that the region included between the origin of these fibers and the internal 

 capsule presents somewhat the form of a pyramid with four sides, Charcot designated it the 

 pyramidal region and the fibers composing it the pyramidal tract. The base of the pyramid in- 

 cludes the convolutions of the cortex in front of the Rolandic fissure. The summit of the 

 pyramid is truncated and covers the pyramidal region of the internal capsule. 



