THE NERVOUS SYSTEM 467 



King considers that one of the two well-marked motor paths in 

 the sheep represents the rubro-spinal tract of some other animals. 

 This tract in the dog is referred to above. 



The Proprio-spinal descending tract or tracts consists of fibres 

 which connect the more anterior spinal segments with the more 

 posterior. The fibres of these in the dog are much more 

 numerous than the pyramidal tract fibres, and their importance 

 lies in the fact that they connect the four limbs together in 

 locomotion. 



Ascending Tracts. — These are as follows : 



The Direct or Dorsal Cerebellar Tract (tract of Flechsig). 

 The Median Superior Tract (column of Goll). 

 The Lateral Superior Tract (column of Burdach). 

 The Ventro-lateral Ascending or Ventral Cerebellar Tract 

 (tract of Gowers). 



The Direct or Dorsal Cerebellar Tract (Fig. 139, A) arises in the 

 peculiar group of cells in the grey matter on the inner side of the 

 dorsal horn. The axons from these cells run to the cerebellum 

 without crossing. This tract forms a long afferent path, and it has 

 been made out that the fibres from the lumbar portion of the cord 

 lie outermost ; the dorsal fibres lie within these ; and, finally, the 

 fibres from the anterior dorsal and lowest cervical nerve are most 

 inwardly placed. The whole of the fibres comprising this tract 

 do not reach the brain ; many terminate in the cord. The tract 

 terminates in the cerebellum, which it enters by the posterior 

 peduncle. 



The Median Superior Tract lies on either side of the dorsal 

 median fissure. The fibres composing it are small, and the 

 path terminates at the bulb. Degeneration of the tract occurs 

 when the dorsal roots of the cord are divided. This tract is 

 made up of long fibres of the dorsal roots of the tail, pelvis, and 

 hind-limbs, and runs up and ends mainly in the bulbar nucleus 

 of Goll, often called the leg nucleus. In Fig. 139, A, this tract cor- 

 responds to the sensory path marked ' hind-leg ' and ' tail.' 



The Lateral Superior Tract is derived from long fibres of the 

 dorsal roots of the thoracic region, fore-limbs, and neck. It 

 runs up and ends mainly in the bulbar nucleus of Burdach 

 {nucleus cuneatus) commonly spoken of in man and the monkey 

 as the arm nucleus. In Fig. 139, A, this sensory path is indicated 

 by the portion marked ' fore-leg,' ' neck,' and ' trunk.' 



The Ventro-Lateral Ascending, or Ventral Cerebellar Tract. — The 

 precise seat of origin of this tract in the cord is unknown. 

 Division of the dorsal roots of the spinal nerves produces no effect 

 upon it. Its origin must therefore be within the cord. The 

 tract terminates in the cerebellum, entering by the anterior 



