548 THE NERVOUS SYSTEM 



in shape on cross-section, and diminishes in size from the cervical region 

 downward. The tract is particularly well marked out, both by the degener- 

 ation and by embryological methods. The fibers are supposed to pass off 

 as they descend, and to join the various local nervous mechanisms of nerve 

 cells and their branchings which are represented in the anterior columns of 

 the cord. The fibers of which this tract is composed are moderately large, 

 but are mixed with some that are smaller. 



The Anterior Pyramidal Tract. This tract is situated in the anterior 

 funiculus by the sides of the anterior fissure, figure 360, 10. It is smaller 

 than the lateral tract and is not present in all animals, though conspicuous 

 in the human cord and in that of the monkey. It can be traced upward to 

 the cerebral cortex, and downward as far as the mid or lower thoracic region, 

 where it ends. 



Antero-lateral Descending Tract. This is an extensive tract, elon- 

 gated but narrow, and reaching from the lateral pyramidal to the anterior 

 pyramidal tract. It is a mixed tract, since not all of its fibers degenerate 

 below the lesions. 



Comma Tract. This is a small tract of fibers in the posterior funiculus 

 which degenerates below the point of section of,, the cord. It consists of the 

 descending collaterals of the posterior ner^gitfcfts as they pass into the cord. 



Tracts of Ascending Degeneration. The fasciculus gracilis, tract of 

 Goll, and the fasciculus cuneatus, tract of Burdach. These tracts degenerate 

 upward on section of the cord, also on section of the posterior nerve roots, 

 figure 362, i. They exist throughout the whole of the cord and can be traced 

 into the bulb. They are sensory tracts, see page 561. 



The Fasciculus Cerebello-spinalis, or Direct Cerebellar Tract. This 

 tract is situated on the outer part of the cord between the lateral pyramidal 

 tract and the margin. It is found in the cervical, thoracic, and upper 

 lumbar regions of the cord, and increases in size from below upward. It 

 degenerates on injury or section of the cord itseli, but not on section of the 

 posterior nerve roots, since its fibers arise from the cells of the dorsal nucleus. 

 As the name implies, it is believed to pass up into the cerebellum, see 

 Page 572, 



The Fasciculus Antero-lateralis, Tract of Gowers. This tract lies 

 at the margin of the lateral funiculus of the cord and extends the full length, 

 see figure 364. 



It will thus be seen that the three general divisions of the white matter 

 of the spinal cord the anterior, the lateral, and posterior funiculi are 

 subdivided into tracts in which the fibers degenerate upward, those in which 

 the fibers degenerate downward, and still others in which the fibers degener- 

 ate either way for only short distances when the cord is cut across. These 

 latter parts of the cord are composed of association fibers which connect 

 different levels of the cord. The association tracts form the antero-laterai 



