500 



THE SPINAL CORD. 



upper part than in the middle of the dorsal region. In the upper 

 part of the cervical region a group of cells reappears in the same situa- 

 tion, and is traversed by the roots of the spinal accessory nerve. The 

 cells of the intermedio-lateral tract are of large and medium size, and 

 many of theiii are fusiform, lying transversely. They are probably con- 

 nected with fibres which run transversely from the commissure across 

 the central portion of the grey substance. 



Commissures. — The anterior commissure consists of medullated 

 nerve fibres which pass on each side, some into the anterior white 

 column, others into the anterior horn. Their course is not strictly 

 transverse, many fibres which enter the anterior part of the commissure 

 at one side leave it at the posterior portion on the other side. There is 

 thus a double decussation at the middle line (fig. 350). Sometimes part 

 of the fibres have an ascending or descending direction, or are displaced 

 by the vessels which pass into the cord from the anterior fissure. 



The i)OsteriQr commissure is composed of fine grey nerve fibres, 

 running transversely and most abundant behind the central canal. On 

 each side of the canal is an area occupied chiefly by gelatinous substance, 

 in which are a few longitudinal fibres and granules. Close to the 

 canal many small round or angular cells are scattered, some branching, 

 others containing many nuclei (probably connective tissue cells). 



The central canal is lined with a layer of cylindrical ciliated epithe- 

 lium. In the adult its lumen is not unfrequently occupied by cells and 

 granular material, and, the epithelium layer being indistinct, the cells 

 within it appear continuous with those in its vipinity. 



The filnm terminale is said to contain in its upper portion a con- 

 tinuation of the central canal, surrounded by gelatinous substance and 

 nerve fibres. In its lower portion it consists of connective tissue only. 



Fig. 352. Fig. 352.— A Small Por- 



tion OF A TRANSVERSE 



Section op the Spinal 

 Cord at the place 

 where two bundles op 

 THE Fibres op the An- 

 terior Roots pass into 

 the grey substance. 



\ \ \IA\v\\>'^^^V\X:-u-v:\ SA~M_l//n5^K<--V" rpijig gg^^j-e may be looked 



upon as reiDresenting the 

 inner ends of the anterior 

 roots of the nerves, of 

 which the outer part is 

 shown in fig. 346. a, a, 

 the two bundles of fibres of 

 the anterior root passing 

 between the compartments 

 of longitudinal fibres of the 

 cord ; b, b, the same fibres 

 running backwards througli 

 the grey substance towards 

 the posterior cornua ; c, c', 

 those spreading in the anterior cornua, on the one side towards the anterior commissure, 

 and on the other round the outer side of the anterior cornu ; d, d, portions of three com- 

 partments of the anterior columns in which the longitudinal fibres of the cord are sliown 

 in transverse section ; e, e, large radiated and nucleated cells in the grey substance of the 

 anterior cornu- -some with three, others with a greater number of processes emanating 

 from them : no direct communication is shown between these processes and the nerve 

 fibres of the roots. 



