CH. XLII.] 



REGIONS OF THE SPINAL CORD. 



617 



commissure is short and extremely narrow. The cord is circular on trans- 

 verse section. 



At the upper part of the conns medttllarit, which is the portion of the cord 

 immediately below the lumbar enlargement, the grey substance occupies 

 nearly the whole of the transverse section, as it is only invested by a thin 



Fig. 457. The above diagrams are reproductions of photo-micrographs from the spinal 

 cord of a monkey in which the operation of left hemiaectiun had been performed 

 some weeks previously (Mott). The sections were stained by Weigert's method, by 

 which the grey matter is bleached, while the healthy white matter remains dark blue. 

 The degenerated tracts are also bleached. A in a section of the cord in the thoracic 

 region below the lesion ; the crossed pyramidal tract is degenerated. B is a section 

 lower down in the lumbar enlargement ; the degenerated pyramidal tract is now 

 smaller. C is a section in the thoracic region some little distance above the lesion. 

 The degenerated tracts seen are in the outer part of Qoll's column and in the direct 

 cerebellar tract. I) is a section higher up in the cervical region ; the degeneration in 

 QoU'scolumn now occupies a median position ; the degenerations in the direct cerebellar 

 tract, and in the tract of Gowers are also well shown. Notice that in all cases, the 

 degenerated tract* are on the same side as the injury. 



layer of white substance. This thin layer is wanting in the neighbourhood 

 of the posterior nerve-roots. The grey commissure is extremely thick. 



At the level of the Jifth sacral nerve the grey matter is also in excess, 

 and the central canal is enlarged, appearing T-shaped in section ; whilst in 

 the vpi>i-r port inn ofthefilnm terminals the grey matter is uniform in shape 

 without any central canal. 



