880 THE FEATURES OF DIFFERENT REGIONS. [BOOK in. 



matter is not formed by all the fibres from the nerves which join 

 the spinal cord continuing to run along the cord up to the brain ; 

 as we have seen, some at least of the fibres end in the grey 

 matter. Nevertheless the white matter in passing up the cord 

 appears to receive a permanent addition at the entrance of each 

 nerve. We may infer that each nerve has a representative of 

 itself starting from the level of its entrance and running up to 

 some part of the brain. Whether the fibres thus representative 

 of the nerve are continuations of the very fibres of the nerve 

 itself, or are new fibres starting from some relay of grey matter, 

 with which the fibres of the nerve are also connected, is another 

 question. 



571. The grey matter in contrast to the white matter 

 shews great variations in area along the length of the cord (Fig. 

 102). From the entrance of the coccygeal nerve upwards the area 



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FlG. 102. DlAGBAM SHEWING THE VARIATIONS IN THE SECTIONAL AREA OF THE GREY 

 MATTER OF THE SPINAL CORD, ALONG ITS LENGTH. 



increases very rapidly, reaching a maximum at about the level of the 

 5th lumbar nerve. It then rapidly decreases to about the level 

 of the llth thoracic nerve, maintains about the same dimensions all 

 through the thoracic region, and begins to increase again at about 

 the level of the 2nd thoracic nerve. Its second maximum is 

 reached at about the level of the 5th or 6th cervical nerve, after 

 which the area again becomes smaller, remaining however at the 

 upper cervical region much larger than in the thoracic region. 

 The meaning of these variations becomes clear when we turn 



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FIG. 103. DIAGRAM SHEWING THE RELATIVE SECTIONAL AREAS OF THE SPINAL NERVES, 



AS THEY JOIN THE SPINAL CORD. 



to Fig. 103, which shews in a similar diagrammatic manner the 

 sectional areas of the several spinal nerves. It will be observed 

 that the increase and decrease of the sectional area of the grey 

 matter follow very closely the increase and decrease of the quantity 



