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A TEXTBOOK OF PHYSIOLOGY 



The white matter of the spinal bulb consists of conducting tracts, 

 both ingoing and outgoing. The chief ingoing afferent paths are 



1. The mesial fillet. The fibres of this tract arise from the gracile 

 and cuneate nuclei, immediately cross the middle line and pass up 

 in close proximity to and on either side of it (Fig. 396). This 

 crossing forms the sensory decussation; the fibres of the fillet eventu- 

 ally reach the optic thalami (Fig. 434). 



2. The cerebellar tracts of the cord pass up through the medulla 

 to reach the cerebellum (Fig. 431). They occupy part of the area 

 known as the reticular formation (formatio reticularis). 



3. The spino-thalamic tract passes through, and joins with, the 

 mesial fillet to reach the thalamus. 



Fio. 423. PLAN OF THE ORUUN OF THE TWELFTH AND TENTH NEKVES. 

 (A. E. Schafer.) 



pyr., Pyramid; n.XII., nucleus cf hypoglcssal; XII., hypoglossal nerve; d.n.X.XI., 

 dorsal nucleus of vagus and accessory; n.amb., nucleus ambiguus ;/.., fasciculus 

 solitarius (descending root of vagus and glosso-pharyngeal; f.s.n., its nucleus; 

 X., issuing fibres of vagus; y, ganglion cell in vagus giving origin to a sensory 

 fibre; d.V., descending root of fifth; c.r., corpus restiforme. 



4. The external and internal arcuate fibres, which arise from the 

 gracile and cuneate nuclei, and pass to the cerebellum either by an 

 external course from the opposite side or by an internal course from 

 the same side. 



The outgoing fibres take part in the formation of the chief reflex 

 arcs (Fig. 397) : 



1. The vestibulo-spinal, which arises in the upper part of the 

 medulla in Deiters' nucleus. 



2. The rubro-spinal, coming from the red nucleus of the mid- 

 brain. 



3. The pyramidal tracts from the cerebral cortex. These lie 

 anteriorly throughout the great part of the medulla, but in its lo\\ < r 



