MINUTE STEUCTURE. 



499 



In the posterior cornu the large cells are collected chiefly into a 

 compact group, the posterior vesicular column (of Clarke) (fig. 350, c), 

 Vv'hich occupies the inner half of the cervix. The cells lie among fine 

 interlacing fibres, some horizontal, derived chiefly from the jjosterior 

 roots of the nerves, and many longitudinal. Some cells are small and 

 others large, with processes running in different directions, but especially 

 upwards and downwards, parallel to the vertical fibres. This group 

 is skirted by fibres (also chiefly from the posterior roots) which curve 

 around it, and among which lie other fusiform nerve-cells. This group 

 of cells is largest near the upper part of the lumbar enlargement 

 (fig. 348, L 1), where it has a diameter of -^^t\\ of an inch, and causes a 

 projection on the inner surface of the cervix cornu. It can be traced 

 upwards through the dorsal region, becoming less distinct, and ceasing 

 before the middle of the cervical enlargement is reached. Below the 

 middle of the lumbar enlargement it is indistinct. In the upper part 

 of the conns meduUaris a group of cells behind the central canal, on 

 each side, occupies nearly the position of this column, but has different 

 histological connections. (Clarke.) 



In the outer portion of the grey matter, midway between the anterior 

 and posterior cornua, is a small group of cells, the tractus intermedio- 

 lateralis (of Clarke) (fig. 350, cT), which occupies a projection on the sur- 

 face of the grey matter. It extends from the upper part of the lumbar 

 to the lower part of the cervical enlargement, being larger in the 



Fiff. 351. 





o 

 .1 00 



®J 





fe'l0.Qo®nO 





loiJ 



-^^ 





Fig. 351. — A Small Portion of a Transverse Section of the human Spinal Cord 



NEAR THE SuRFACK AT THE ENTRANCE OF A BuNDLE OF THE ANTERIOR RoOTS. (Allen 



Thomson.) -°" 



This figure, which is somewhat diagrammatic, is intended to show the relation to the 

 nervous substance of the pia-matral sheath of the cord aud the processes of connective 

 tissue prolonged from it between the longitudinal and other nerve fibres, a, a, a bundle 

 of the anterior roots ; b, h, transverse sections of part of the anterior columns of the 

 cord in which the dark points are the axis-cylinders, and the circles represent the outline 

 of the medullary substance : in these parts the connective tissue is not represented, and 

 many of the smallest nerve-fibres have also, for the sake of clearness, been omitted ; 

 c, the pia-matral covering of the cord ; d, one of the compartments of the anterior 

 column enclosed by septa of connective tissue prolonged from the pia mater, and exhibit- 

 ing the fine frame-work of connective tissue, c, e, extending through among the nerve- 

 fibres, which last have been omitted. 



K K 2 



