382 NORMAL HISTOLOGY AND ORGANOGRAPHY. 



begins, the crossed pyramidal comes to the surface 

 of the cord. The fibers of this tract have their origin 

 in the large pyramidal cells of the cerebrum in the 

 region of the area of Rolando. Traced downward 

 from this source, they cross in the lower part of the 

 medulla to the opposite side of the cord, making at 

 this point the motor decussation. As it descends the 

 tract gradually diminishes in size, due to the fact 

 that fibers leave it to arborize around the large 

 motor cells of the anterior horn. In this way the 

 entire tract is ultimately exhausted near the lower 

 extremity of the cord. It is thus a descending or 

 motor tract that governs the opposite side of the 

 body from where it has its origin. 



4. LowenthaVs tract is closely associated with 

 Gowers's. Its position is anterior and mesial to 

 Gowers's, encroaching some upon the anterior region 

 of the cord. The fibers of this tract are supposed to 

 come from cells in Deiters' nucleus of the medulla 

 which may be regarded as an internode between the 

 cerebellum and the medulla. This tract descends 

 as far as the lumbar region and its fibers are supposed 

 to arborize around the motor cells of the anterior 

 horn of the spinal cord. 



5. The mixed lateral bundle represents the re- 

 mainder of the lateral region. Its fibers probably 

 come from cells in all parts of the gray matter of the 

 cord, and from cells on the opposite side of the cord. 

 At intervals these fibers ultimately reenter the gray 

 matter and arborize about nerve cells. It is there- 

 fore an intersegmental or commissural tract, both 

 sensory and motor. 



