THE DISSECTION OF THE BACK 197 



surface. The thickened end of the anterior column is termed 

 the caput columnar anterioris, and the constricted part close to 

 the grey commissure is called the cervix columns anterioris. 

 The posterior grey column in most localities is elongated and 

 narrow. Further, it is drawn out to a fine point, which almost 

 reaches the bottom of the postero- lateral sulcus. This 

 pointed extremity receives the name of the apex columns 

 posterioris ; the slightly swollen part which succeeds it is 

 the caput columnae posterioris ; whilst the slightly constricted 

 part adjoining the grey commissure goes under the name of 

 the cervix columntz posterioris. 



Covering the tip of the posterior column there is a substance 

 which differs in its composition from the general mass of grey 

 matter, and presents a translucent appearance. It is termed 

 the substantia gelatinosa (Rolandt). 



The grey matter is not present in equal quantity through- 

 out the entire length of the medulla spinalis. Therefore it is 

 necessary that it should be considered in different regions, and 

 it must be understood, when the terms cervical, lumbar, sacral, 

 etc., are applied to different portions of the spinal medulla, 

 that these terms apply to the regions to which the nerves of 

 the same name are attached. 



Wherever there is an increase in the size of the nerves 

 attached to a particular part of the medulla spinalis, there a 

 corresponding increase of the grey matter may be noticed. It 

 follows from this that the districts in which the grey matter 

 bulks most largely are the lumbar and cervical swellings. 

 The great nerves which go to form the limb plexuses enter 

 and pass out from those portions of the medulla spinalis. In 

 the intermediate thoracic region there is a reduction in the 

 quantity of grey matter, in correspondence with the smaller 

 size of the thoracic nerves. 



The shape of the crescentic masses of grey matter is not 

 the same in all regions. In the thoracic region both columns 

 are narrow, although the distinction between the anterior grey 

 column and the more attenuated posterior grey column is still 

 sufficiently manifest. In the cervical region the contrast 

 between the grey columns is most marked ; the anterior grey 

 column is very thick in comparison with the posterior grey 

 column. In the lumbar region, on the other hand, the 

 difference in the thickness of the two grey columns is not 

 nearly so apparent, owing to a broadening out of the 



n136 



