472 THE ORGANS 



of the posterior or medial longitudinal fasciculus. It is uncrossed 

 and lies near the floor of the brain cavity and next the median line. 

 In the cord it occupies a similar position near the ventral sulcus- 

 Its fibres terminate in the ventral horn. Some fibres have been 

 traced into the lumbar cord. (Figs. 326 and 358.) 



IV. The Rubro-spinal Tract {von Monakow's Tract). — This con- 

 sists of axones of the red nucleus (nucleus ruber) located in the teg- 

 mentum of the midbrain. These axones cross and descend to the 

 cord, being joined by axones of the other cells in the reticular forma 

 tion in the region of the pons. In the cord the tract lies mingled with 

 and ventral to the lateral pyramidal tract. Its fibres terminate in the 

 dorsal part of the ventral horn. This tract is a lower link in a three- 

 neurone path from cerebellum to cord composed as follows: (a) 

 Axones of cells in cerebellar cortex to nucleus dentatus in cerebel- 

 lum; (b) axones of cells in nucleus dentatus via superior cerebellar 

 peduncle to the nucleus ruber; (c) axones of nucleus ruber as the 

 rubro-spinal tract to (d) efferent peripheral neurones of cord. (Figs. 

 326, 331 and 345.) 



V. The Deitero-spinal Tract {Vestihulo-spinal Tract).- — This 

 tract originates from Deiters' nucleus which lies in the medulla and 

 receives fibres from the vestibular division of the acoustic nerve 

 and also from the cerebellum (see below). It occupies the ven- 

 tral and mesial periphery of the cord. The more lateral fibres are 

 uncrossed, those near the ventral sulcus come from the nuclei of 

 both sides. Descending with these fibres are probably axones of 

 other vestibular terminal nuclei, and of other nuclei in the gray re- 

 ticular formation (reticulo-spinal fibres) of the medulla. These fibres 

 all terminate in the ventral horn. Some fibres have been traced to 

 the sacral cord. Deiters' nucleus receives fibres from the cerebellum, 

 and thus this tract is a segment of a second efferent cerebellar path- 

 way: (a) Axones of cells in cerebellar cortex to nucleus fastigii in 

 cerebellum; {b) Axones of cells of nucleus fastigii as the fastigio- 

 bulbar tract to Deiters' nucleus; (c) axones of cells of Deiters' nucleus 

 as the Deitero-spinal tract to (d) efferent peripheral neurones of 

 cord. According to some authorities some fibres proceed from 

 cerebellum to cord without interruption in Deiters' nucleus. (Figs. 

 326 and 331.) 



All the fibres of V are sometimes collectively called the antero- 

 lateral descending tract or marginal bundle of Lowenthal. 



Tract III and the mesial part of V constitute the major portion of 



