THE NERVOUS SYSTEM 473 



the descending fibres of an important bundle in the segmental brain 

 known as the medial longitudinal fasciculus. 



VT. The Fasciculus of Thomas. — Besides the reticulo-spinal fibres already 

 mentioned are hljres in llie lateral column which originate in the reticular forma- 

 tion of the medulla and terminate in the gray of the cervical cord. These are 

 known as the tract of Thomas. (Fig. 326.) 



VII. Helweg's tract is a small triangular bundle of fibres lying along the 

 ventro-lateral margin of the cord, and is traceable upward as far as the olives 

 (Fig. 326). The origin and destination of its fibres are not definitely known. 

 Some of its fibres appear to originate in the cord and terminate in the inferior 

 olivary nucleus in the medulla (spino-olivary fibres). 



VIII. The Septo-marginal Tract. — This is a small bundle of fibres lying next 

 the posterior septum. It appears to change its location in different levels, 

 e.g., in the sacral cord it occupies a small dorso-median triangle, in the lumbar 

 region it forms an oval bundle (of Flcchsig) at the middle of the septum and a 

 superficial bundle, in the thoracic and cervical cord its fibres are more scattered. 

 It is probably composed of descending axones of ceils in the cord. (Fig. 326.) 



IX. The so-called "comma" tract of Schultze is a small comma-shaped 

 bundle of descending fibres lying about the middle of the posterior column (Fig. 

 326). It is most prominent in the dorsal cord. Its fibres are believed by some 

 to be descending branches of spinal ganglion cells, by others to be descending 

 axones from ceUs situated in the gray matter of the cord (column cells). 



In general the descending tracts fall into two categories: (i) 

 Tracts which are descending or efferent suprasegmental paths, or are 

 parts of such paths. These comprise (a) the efferent pallial path 

 (tract I), {h) the efferent midbrain paths (tracts II and III) and (c) 

 the efferent cerebellar paths (tracts IV and V) . (2) Descending inter- 

 segmental tracts. Of the latter some originate in nuclei lying in the 

 segmental brain (nucleus of the medial longitudinal fasciculus, 

 nucleus ruber, nucleus of Deiters) which receive efferent supraseg- 

 mental fibres, and thus form links of descending suprasegmental paths. 

 Other reticulo-spinal fibres come from other cells in the gray reticular 

 formation. Other still shorter tracts (spino-spinal) , from cells in the 

 cord, form the descending fibres in the ground bundles (see below). 

 Tracts VIII and possibly IX are also in this category. 



The descending path from the pallium which terminates around 

 the bodies of the splanchnic efferent neurones in the cord is stated 

 to consist of two neurones, a pallio-bulbar neurone to the medulla and 

 a bulbo-spinal neurone to the efferent peripheral neurone in the cord. 

 The axones of the latter pass out of the cord as preganglionic fibers 

 to the sympathetic ganglion cells. In the cord the fibres of this path 



