OF THE NERVUS OCTAVUS. 121 



mally, has not lesioned there completely the ventral root at its 

 entrance and is consequently more or less isolating the tractus 

 DEITEHS descendens from the descending root (Plate XX fig. 25 G) 

 at the beginning of its course. 



The degenerated fibres of this tract are very thick fibres and 

 may easily be followed towards the nucleus of DEITERS in case of 

 partial destruction (in fig. 25 at the right side). 



During its distal course this field of degenerate fibres is lying 

 in the middle of the formatio reticularis. In frontal sections it has 

 the form of a triangle , its top is directed dorsally and its base 

 resting upon the facial nucleus. 



More distally, the facial nucleus having disappeared it tends to 

 take a more ventral position. In the level of the oliva inferior, 

 it reaches the nucleus para-olivaris resting upon its lateral border. 

 Medially the area is bordered by the issuing rootfibres of the 

 XII th nerve. There it reaches nearly the peripherical margin of 

 medulla oblongata (Plate XX fig. 25 I and K). 



At the distal end of the medulla oblongata it is found at the peri- 

 pherical margin, bordered medially by the roots of the 1 th spinal 

 ventral root. Its form (Plate XX fig. 25 L) is still that ot a 

 triangle, with its basis at the ventral margin of the lateral column, 

 its short side towards the formatio reticularis of the cornu lateralis, 

 to which it leaves collaterals. 



At the entrance of the second spinal ventral root it has a posi- 

 tion still more at the peripherical antero-lateral margo of the cord 

 (Plate XXI fig. 25 M). 



The diagram of the degenerated tract now has the form of a 

 spherical obtuse-angled triangle, the basis of which lays at the 

 antero-lateral margin of the cord, for its ventral edge now is no 

 longer bordered medially by the entering roots and reaches into 

 the columna anterior. 



In this way the basis extends along the ventral third part of the 

 lateral margin. There the short side of the triangle leaves the mar- 

 gin under an obtuse angle, curving towards the lateral cornu in 

 a ventrally concave curvation. Its top now nearly reaches the 

 ventral portion of the formatio reticularis of the lateral horn, and 

 from there parts the long side of the triangle, sligtly arched and 

 concentric to the border of the cornu antero-lateralis and concave 

 towards the median line, it returns under a sharp angle, towards 

 the ventral end of the basis. 



During its distal course through the cord, the diameter of this 

 degenerated area changes. In its way through the intumescentia 



