THE SPINAL CORD 551 



situated at different levels are united anatomically and associated for 

 the performance presumably of complex reflex activities. 



In the dorsal funiculus there are two well-defined fasciculi or tracts of 

 fibers which belong in all probability to the associative tracts, viz.: the 

 " comma tract" and the sep to-marginal tract. The comma tract described 

 by Schultze is found in the border region of the dorso-external and the 

 dorso-internal tracts (see below). It originates in the cervical region and 

 descends into the thoracic region. When divided transversely, it de- 

 generates downward. 



The septo-marginal tract is situated along the median surface of the 

 dorso-external tract. These two tracts associate more or less distant 

 regions of the cord. 



The Ascending Tracts or Fasciculi. The ascending tracts are found 

 for the'most part in the dorsal and lateral funiculi, though a few are found 

 in the ventral funiculus. 



The ascending tracts present in the dorsal funiculus proceeding from 

 behind forward may be divided into two main groups, viz.: the dorso- 

 internal and the dorso-external. 



1 . The Dorso-internal Tract or Fasciculus of GolL This tract lies close to 



the dorso-median fissure and consists of nerve-fibers which are the 

 continuations of the dorsal roots of the sacral, lumbar and lower 

 thoracic nerves of the same side. After entering the cord they pass 

 upward as far as the lower portion of the medulla oblongata where 

 their terminal branches arborize around the cells of a nucleus known 

 as the clavate or gracile nucleus. 



2. The Dorso-external Tract or Fasciculus of Burdach; This tract lies just 



within the dorsal horn and is separated from the dorso-internal tract 

 by a septum of connective tissue most marked above the eleventh 

 thoracic segment. The fibers composing this tract are the continua- 

 tions of the dorsal roots of the upper thoracic and cervical nerves. 

 After entering, they cross the cord obliquely and pass upward as far 

 as the lower border of the medulla oblongata where their terminal 

 branches arborize around the cells of a nucleus known as the cuneate 

 nucleus. Transverse division of the fibers of these tracts is followed 

 by a degeneration upward as far as the cuneate and clavate nuclei, 

 indicating that their trophic center is situated at a lower level. 



3. The Poster o -marginal Tract or Tract of Lissauer. This tract of fibers is 



composed chiefly of fibers derived from the dorsal roots of the spinal 

 nerves and embraces in part the tip of the dorsal horn. After enter- 

 ing this tract the terminal of the fibers arborize around nerve-cells in 

 the dorsal horns. Associative fibers are also intermingled. 

 The ascending tracts present in the lateral funiculus are six in number 



as follows: 



i. The Dorsal Spino-cerebellar Tract, or Tract of Flechsig. This tract or 

 fasciculus lies on the dorsal aspect of the lateral funiculus. It slightly 

 increases in size from the level of the second lumbar nerve up to the 

 medulla oblongata. It is composed of nerve-fibers that have their 

 origin in the nerve-cells composing the vesicular column of Clark on 

 the same side. From their origin the fibers pass obliquely outward 

 to the surface, then turn upward and finally by way of the inferior 



