POSTERIOR FUNICULUS 



781 



undergo a Y-shaped bifurcation in the neighbourhood of the dorsal horn, one 

 branch ascending and the other descending. Their ascending branches form the 

 fasciculus gracilis (GoU's column) and thefasciculuscuneatus(Burdach's column). 

 These fasciculi are the chief ascending or sensory spino-cerebral connections, the 

 direct sensory path to the brain. The neurones represented in them con- 

 stitute the first link in the neurone chain between the periphery of the body and 

 the cerebral cortex. 



Fig. 617. — Showing Disposition of the Dorsal Root Fibres Upon Entering the Spinal 



Cord. (From Ediager, after Cajal.) 



A, shows dorsal root axones DR, entering the spinal cord, bifurcating at B, and giving off collat- 

 erals C to the neurones of the cord. B shows the telodendria of these axones or of their 

 collaterals displayed upon cell-bodies of the grey substance of the cord. 



In threading their way toward the brain, these sensory axones tend to work toward the mid- 

 line. Therefore those of longer course are to be found nearer the posterior septum, in the upper 

 segments of the cord, than those axones which enter the cord by the dorsal roots of the upper 

 segments. Thus it is that the fasciculus graciUs, the medial of the two fasciculi, contains the 

 axones which arise in the spinal gangha of the sacral and lumbar segments. In other words, it is 

 the fasciculus bearing sensory impulses from the lower limbs to the brain, while the fasciculus 

 cuneatus, the lateral of the two, is the corresponding pathway for the higher levels. Naturally, 

 there is no fasciculus cuneatus as such in the lower segments of the spinal cord. The axones 

 being much blended at first, it is only in the upper thoracic and cervical region that there is 

 any anatomical demarcation between the two fasciculi. In this region the two become so dis- 

 tinct that there is in some cases an apparent connective-tissue septum between them, continuing 

 inward from the postero-intermediate sulcus — the surface indication of the Une of their junction 

 (fig. 616). 



Upon reaching the medulla oblongata the fibres of the fasciculus gracilis and the fasciculus 

 cuneatus terminate about cells grouped to form the nuclei of these fascicuh. The nucleus of the 

 fasciculus gracilis is situated medially and begins just below the point at which the central canal 

 opens into the fourth ventricle; the nucleus of the fasciculus cuneatus is placed laterally and ex- 

 tends somewhat higher than the other nucleus. The neurones whose ceU-bodies compose these 



