212 ELEMENTS OF MAMMALIAN ANATOMY. 



matter. Its fibers originate from the cells of the more 

 central portion of the gray matter throughout the cord 

 and terminate in the cerebellum. Its fibers help to 

 form the inferior peduncle of the cerebellum. 



The ant ero -lateral descending cerebellar tract occupies 

 the superficial area ventrad of the anterior horn of gray 

 matter. Its fibers originate in the cells of the cerebellum 

 and extend caudad in the cord. 



The antero-lateral ascending cerebellar or Gowers's 

 tract occupies the superficial area laterad of the anterior 

 horn. Its fibers probably originate in the cells of central 

 gray matter throughout the cord, and largely terminate 

 in the cerebellum. The lateral ground bundle consists 

 largely of fibers with a short course, many of which are 

 commissural, connecting the two halves of the spinal cord. 



The crossed pyramidal tract contains the longest 

 fibers of any of the tracts of the central nervous system 

 and occupies a large area just laterad of the posterior 

 horn of gray matter. Its fibers originate in the cortical 

 cells of the brain near the crucial sulcus (Fig. 89), and 

 descend as part of the internal capsule, through the 

 corpus striatum and laterad of the optic thalamus to the 

 base of the brain. Here it is one of the three main tracts 

 forming the crus or peduncle of the cerebrum, whence 

 it extends through the pons Varolii, appearing along the 

 median ventral line of the medulla as the pyramid (Fig. 

 90). At the caudal end of the medulla it crosses dorsad 

 to the opposite side of the cord to occupy the area laterad 

 of the posterior horn of gray matter. Its fibers terminate 

 largely in arborizations around motor cells of the cranial 

 nerves in the brain, and the cells in the anterior horn 

 of gray matter, from which originate the motor fibers 

 for the muscles of the body. Therefore it is apparent 

 that this tract controls largely the muscular activities 



