Till-: .S'/'/.Y.I/. CORD 7o7 



into tne spinal cord and their terminations noted either l>y collateral or terminal twigs, or the 

 fasciculus they join in their cephalic course may be determined. 



For topographical purposes, that the various fasciculi may be referred to with greater case, the 

 white substance of the spinal cord in .-eel ion is divided into three areas known as funiculi or col- 

 umns and which correspond to the funiculi already mentioned as evident upon the siirtaee ot the 

 cord when intact. The funiculi are outlined wholly upon the basis of their position in the cord 

 and with reference to the median line and the contour of the column of urey substance; their com- 

 ponent fasciculi are defined upon the basis of function. (1) The posterior junitulus or column is 

 bounded by the posterior septum and the line of the dorsal horn; (2) the lateral funieulus or 

 column is bounded by the lateral concavity of the grey column and the lines of entrance and exit 

 of the dorsal and \entr,d roots; (:(i the r,ntral juniculus or column is bounded by the mesial border 

 of the ventral horn and by the anterior median fissure. 



The posterior f uniculus or column. This column is composed of two general va- 

 rieties of axones arranged in five fasciculi. First, and constituting the predominant 

 type in all the higher segments of the cord, are the afferent or general sensory axones, 

 which arise in the spinal ganglia, enter the cord by the dorsal roots, assume their dis- 

 tribution to the neurones of the cord, and then take their ascending course towards 

 the encephalon. The axone of the spinal ganglion neurone undergoes a T-shaped divi- 

 sion a short distance from the cell-body, one limb of this division terminating in the 

 peripheral organs and the other going to form the dorsal root. Upon entering the cord 

 the dorsal root axones 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 (doll's column) and the fasciculus cunea- 

 tus f Bunlarh's column). These fasciculi are the chief ascending or sensory cerebro- 

 spinal connections, the direct sensory path to the cerebrum. The neurones repre- 

 sented in them constitute the first link in the neurone chain between the periphery 

 of the body and the cerebral cortex. In threading their way towards the brain, 

 these sensory axones tend to work towards 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 gracilis, the medial of the two fasciculi, contains the 

 axones which arise in the spinal ganglia of the sacral and lumbar segments. In other 

 words, it is the fasciculus bearing sensory impulses from the lower limbs to the brain, 

 w'nle 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 cervical region that there is any anatomical demarcation between the two fas- 

 ciculi. In this region the two become so distinct that there is in some cases an ap- 

 parent connective-tissue septum between them, continuing inwards from the postero- 

 intermediate sulcus the surface indication of the line of their junction. 



I'pon reaching the medulla oblongata the fibres of the fasciculus gracilis and the 

 fasciculus cuneatus terminate about cells grouped to form the nuclei of these fasciculi. 

 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 extends somewhat higher than the other 

 nucleus. The neurones whose cell-bodies compose these nuclei constitute the 

 second links in the neurone chains conveying sensory impulses from the periphery 

 to the cerebral cortex. 



The descending or caudad branches of the dorsal root axones are concerned wholly 

 with the neurones of the spinal cord. They descend varying distances, some of them 

 as much as four segments of the cord, and give off numerous collaterals on their way 

 to the cells of the grey column. Those terminating about cell-bodies of the ventral 

 horn which give rise to the ventral or motor root-fibres, are responsible for certain 

 of the so-called 'reflex activities' and thus contribute to the simplest of the reflex 

 arcs. In descending they serve to associate different levels of the grey substance 

 of the cord with impulses entering by way of a single dorsal root. Some of their col- 

 laterals cross the mid-line in the posterior white commissure, and thus become con- 

 nected \\itli neurones of the opposite side. The caudad branches of longer course 

 are scattered throughout the ventral portion of the fasciculus cuneatus (middle root 

 zone), but show a tendency to collect along the border-line between the fasciculus 

 cuneatus and the fasciculus gracilis, and thus contribute largely to the comma- 

 shaped fasciculus. Also many of them course in the oval bundle or septo- 

 marginal root zone. 



