276 NORMAL HISTOLOGY. 



Based on the collective results of the anatomical, physiological and 

 developmental methods of study, it is possible to locate and trace with fair 

 accuracy a number of fibre-tracts in the cerebro-spinal axis. Since they are 

 undergoing continual augmentation or decrease, their actual area and posi- 

 tion are subject to variation, so that the detailed relations in one region of 

 the cord differ from those at other levels. The accompanying schematic 

 figure (Fig. 321), therefore, is to be regarded as showing only the general 

 relations of the most important paths of the cord, and not as accurately 

 representing the actual form and size of the fibre-tracts. Further, it must 

 be appreciated that the definite limits of these tracts in such diagrammatic 

 representations seldom exist in reality, since the fibres of the adjacent paths 

 in most cases overlap, or, indeed, extensively intermingle, so that the fields 

 marked in cross-sections may be shared by fibres belonging to differen 

 systems. 



The constitution of the fibre-tracts of the cerebro-spinal axis is mani- 

 festly beyond the province of these pages. For such information the reader 



FIG. 323. Section of cord through lower part of cervical region. X 6. (Preparation by Professor Spiller.) 



is referred to the systematic text-books of anatomy and the special works on 

 the nervous system. A few considerations of importance, however, may 

 here find appropriate mention. 



All afferent or sensory impulses entering the cord do so by way of the 

 posterior root-fibres. The latter are the centrally directed processes (axones) 

 of the neurones whose cell-bodies are the ganglion-cells within the spinal 

 ganglia situated on the dorsal roots of the spinal nerves. These root-fibres 

 convey to the cord the various impulses collected by the peripherally directed 

 processes (the sensory nerves) from the integument, mucous membranes, 

 muscles, tendons and joints from all parts of the body, with the exception of 

 those served by the cranial nerves. Some of the afferent impulses thus con- 

 ducted are transformed in the cerebrum into impressions of touch, pressure- 

 sense and temperature, while others are carried to the cerebellum, which 

 responds by efficient impulses that exercise the restraint necessary to maintain 

 coordination. 



On entering the spinal cord along the postero-lateral sulcus, most of 

 the dorsal root-fibres penetrate the fasciculus cuneatus (tract of Burdach) 



