THE NERVOUS SYSTEM 1435 



dorsal longitudinal bundle. Its fibres are derived from the stratum 

 opticum and stratum lemnisci of the upper quadrigeminal body of 

 the opposite side. These fibres, as stated in connection with the 

 upper quadrigeminal bodies, cross the median plane and decussate 

 with the corresponding fibres of the opposite side, the decussation 

 being known as the fcmntain-decussaiion of Meyneri. The fibres 

 descend through the tegmentimi, Ipng close to the red nucleus, to 

 which they furnish collaterals. Thereafter they traverse the 

 formatio reticularis of the pons Varolii and medulla oblongata, 

 still lying on the ventral aspect of the dorsal longitudinal bundle. 

 From the medulla oblongata the fibres pass into the anterior 

 ground-bimdle of the ventral column of the spinal cord, in associa- 

 tion with the fibres of the dorsal longitudinal bundle, and they 

 form arborizations around the motor cells of the ventral comu of 

 grey matter. 



Rubro-Spinal Traet, or Bundle of Monakow.— The fibres of this 

 tract are derived, as previously stated, from the axons of the cells 

 of the red nucleus. They cross the median plane, decussating with 

 the corresponding fibres of the opposite side, and constituting the 

 fountain-decussation of Ford. The tract then descends through 

 the pons Varolii and medulla oblongata into the lateral colvmm of 

 the spinal cord, in which it constitutes the prepyramidal tract on 

 the ventro-lateral aspect of the crossed p\Tamidal tract. 



Mesial FlUet. — ^The mesial or main fillet of either side, which 

 represents the chief sensory tract, commences in the lower part of 

 the medulla oblongata. It here constitutes the only fillet on 

 either side, and its fibres are derived from the deep lemniscal 

 arcuate fibres, which arise from the cells of the nucleus gracilis 

 and nucleus cimeatus of the opposite side. The main fillet there- 

 fore represents the upward continuation of the posterior column 

 of the spinal cord (columns of Goll and of Burdach), and it 

 is spoken of as the chief sensory traet. The deep lemniscal arcuate 

 fibres, as previously stated, cross the median plane directly above 

 the decussation of the pyramids {motor decussation), and they 

 decussate with the corresponding fibres of the opposite side, thus 

 constituting the decussation of the fillets (main fillets, or chief sen- 

 sory tracts), or the sensory decussation. The fibres, after crossing 

 the median plane, form the fillet of the side to which they have 

 crossed. In the medulla oblongata it lies close to the median 

 raphe, and at first is internal to the dorsal longitudinal bundle. 

 Subsequently, however, the main fillet takes up a position in front 

 of the dorsal longitudinal bundle, and directly behind the p^nramid. 

 The main fillet then ascends through the dorsal part of the pons 

 Varolii, its relative position remaining unchanged. In this situa- 

 tion the lateral fillet, to be presently described, takes up its position 

 on the outer or lateral aspect of the main or mesial fillet. The 

 main fillet, on leaving the pons Varolii, enters the ventral part of 

 the tegmenttmi, still having the lateral fillet on its outer side. As 

 it encoimters the red nucleus, it is displaced outwards and back- 



