6l6 STRUCTURE OF THE SPINAL CORD. [CH. XLII. 



confined to the voluntary muscles, but includes the muscular fibres 

 of the blood-vessels and viscera. Hence there is fall of blood 

 pressure, paralysis of sphincters, etc. 



2. Loss of sensation in the same regions. 



3. Degeneration, ascending and descending, on both sides of 

 the cord. 



Hemisection. If the operation performed is not a complete 

 cutting of the spinal cord across transversely, but a cutting of 

 half the cord across, it is termed hemisection. 



This operation leads to : 



1. Loss of motion of the parts supplied by the nerves below 

 the section on the same side of the body as the injury. 



2. Loss of sensation in the same region. The loss of sensation 

 is not a very prominent symptom, and is limited to the sense of 

 localisation and the muscular sense. The animal can still feel 

 sensations of pain and of heat and cold. 



3. Degeneration, ascending and descending, nearly entirely 

 confined to the same side of the cord as the injury. These are 

 shown in the photo-micrographs (fig. 457) on the opposite page, 

 the small text beneath which should be carefully studied. 



Differences in different regions of the spinal cord. The outline of the 

 prey matter and the relative proportion of the white matter varies 

 in different regions of the spinal cord, and it is, therefore, possible to tell 

 approximately from what region any given transverse section of the 

 spinal cord has been taken. The white matter increases in amount from 

 below upwards. The amount of grey matter varies ; it is greatest in the 

 cervical and lumbar enlargements, viz., at and about the 5th lumbar and 6th 

 cervical nerve, and least in the thoracic region. The greatest development 

 of grey matter corresponds with greatest number of nerve-fibres passing from 

 the cord. 



In the cervical enlargement the grey matter occupies a large proportion 

 of the section, the grey commissure is short and thick, the anterior horn is 

 blunt, whilst the posterior is somewhat tapering. The anterior and posterior 

 roots run some distance through the white matter before they reach the 

 periphery. At the extreme upper part of the cervical region, the end of the 

 posterior horn is swollen out by excess of neuroglia into a rounded mass 

 called the suostantia gelatinosa of Rolando. The cervical cord is wider 

 from side to side than from before back ; this is owing to the great width of 

 the lateral columns. 



In the dorsal region the grey matter bears only a small proportion to the 

 white, and the posterior roots in particular run a long course through the 

 white matter after they enter the cord ; the grey commissure is thinner 

 and narrower than in the cervical region. The intermedio-lateral tract 

 is here most marked, and forms a prominence often called the lateral horn. 

 This is shown in fig. 456 (i T). Clarke's column is also confined to this 

 region of the cord ; the position of the cells which make up this column is 

 shown in the same figure (C c). The cord in this region is circular in 

 transverse section (see also fig. 457 C.). 



In the lumbar enlargement the grey matter again bears a very large pro- 

 portion to the whole size of the transverse section, but its posterior cornua 

 are shorter and blunter than they are in the cervical region. The grey 



