THE NERVOUS SYSTEM 



1321 



cells form longitudinal columns of various lengths, and, as seen in 

 transverse sections of the cord, they are arranged in groups which 

 occupy particular regions. These cell-columns or groups are three 

 in number, namely, anterior or ventral, in the anterior comu of 

 grey matter ; lateral, in the lateral comu of grey matter ; and 

 posterior, constituting the posterior vesicular column of Lockhart 

 Clarke, and being very conspicuous in the mesial portion of the 

 cer\-ix of the posterior grey comu in the thoracic region. Besides 

 these main columns or groups, other ner\'e-cells are present, which 

 are scattered irregularly throughout the other portions of the grey 

 matter. 



The anterior or ventral cell-column is situated, as stated, in 

 the anterior comu of grey matter, and extends throughout the 



Anterior Nerve-Root 

 Anterior Comu 



Central Canal 



Latetal Comu 



Mesial Group of Motor Cells 



Lateral Group of Motor Cells 



„ Cells of Lateral 

 Comu 



Posterior Comu 

 Posterior Nerve-Root 



Clarke s Dors^ 

 Nucleus 



Substantia Gelatioosa 

 Rolandi 



Fig. 553- — Transverse Section of the Spinal Cord in the Upper 

 Thoracic Region, showing the Arrangement of the Grey Matter 

 AND Cells (Semi-diagrammatic) (after Poirier). 



whole length of the spinal cord. Its cells are of large size and 

 very conspicuous, and their axons, which are at first non-medul- 

 lated, become medullated, and then constitute the fascicuH which 

 emerge to form the anterior ner^-e-roots. These cells are therefore 

 the sources from which the efferent or motor ner\'e-fibres proceed, 

 and the ventral column is consequently spoken of as the motor 

 or ganglionic column. The ventral or motor cells of this column 

 are arranged in two groups, mesial and lateral. The mesial group 

 occupies the mesial part of the anterior grey comu, and the lateral 

 group is situated in its outer part. In the cer^ucal and lumbar 

 enlargements of the cord the cells of the lateral group are very 

 numerous, and are arranged in two sub-groups, ventro -lateral and 

 dorso-lateral. 

 The intermedio-lateral cell-column is situated, as stated, in the 



