THE NEUROGLIA AND BLOOD-VESSELS OF THE CORD. 



631 



of the fibres split into an outer and inner part. The lateral smaller part or central fibres (8 to 

 10) passes into the substantia gelatinosa, where it divides into several strands, some of which 

 pass into the central part of the grey matter (10), while others (8) pass upwards and downwards in 

 a longitudinal direction. Some of the fibres (9) perhaps end in the nerve-cells (/) in the posterior 

 cornu. The median, inner or internal radicular fasciculus (11 to 14), sweeps through the 

 postero-external column, and, after running a longitudinal course in the white matter, enters the 

 grey substance of the posterior cornu. Some fibres (11) pass to the small fusiform cells (g) ; 

 and others (13) pass to be connected with the cells of Clarke's column (h), when it is present. 

 From the cells of Clarke's column, fibres seem to pass to the direct cerebellar tract (20). Some 

 of the fibres (12) pass into the posterior grey commissure, to reach the opposite side. This so 

 far only accounts for a part of the fibres. Some of them (8 to 10) are concerned in the formation 

 of the fine nerve-plexus in the grey matter, whereby, perhaps, they become connected with the 

 cells in the anterior cornu. It is asserted that some of the fibres (14) ultimately pass into 

 Goll's column. Many of the fibres in the posterior root have been proved to be directly con- 

 nected with nerve-cells, e.g., in Petromyzon by Freund, and in the Proteus by Klaussner, so 

 that it is very doubtful if, in the higher animals, the fibres of the posterior root are directly 

 connected with the plexus of grey fibres as suggested by Gerlach (p. 629).] 



Neuroglia. The connective-tissue of the spinal cord arises in part from the pia mater and 

 passes into the white matter, carrying with it blood-vessels, and forming septa, which separate 

 the nerve-fibres into bundles. [The connective-tissue of the central nervous system is so far 

 peculiar, that the intercellular substance is reduced to a minimum. It consists of a reticulated 

 connective-tissue composed of fine fibres, which form a network. Fig. 450 shows one of the 



cells, "glia-cells," iso- 

 lated. It consists of a 

 small, granular, nucle- 

 ated body, with numer- 

 ous excessively fine, 

 slightly branched, stiff 

 processes. The pro- 

 cesses form a sustenta- 



451. 



Fig. 



Fig. 450. Fig. 



450. Isolated connective-tissue corpuscle or "glia-cell" from the human spinal cord ; 

 x 800. Fig. 451. Longitudinal section of the spinal cord, a, white, b, grey matter; c, 

 crystals of mercuric chloride. Prepared by Golgi's mercuric chloride method ; x 80. 



cular tissue for the nerve-fibres and blood-vessels. The arrangement and distribution of these 

 cells is best seen in sections of a cord hardened by Golgi's method in corrosive sublimate solution 

 (fig. 451). In some situations, e.g., the white matter of the cerebrum and cerebellum, the cells 

 are smaller and more angular, and the processes are often connected with the outer coat of the 

 blood-vessels. On the whole, the connective-tissue is much finer, in the brain than in the 

 cord. The central canal is surrounded with a denser layer of this tissue, known as the 

 "central ependyma," which stains deeply with carmine, and is very like the substantia 

 gelatinosa in its structure (p. 628). "We must distinguish from this form of connective-tissue 

 that special form in the grey matter to which Virchow gave the name of neuroglia. It is 

 specially adapted to fill up the spaces left by the other elements, and without interfering with 

 the exchange of fluids serves to hold the elements together. It is an excessively finely granular 

 ground-substance in the grey matter. It is also an intercellular substance, but in the adult the 

 cells to which it owes its origin are no longer to be found. It is doubtful, from its chemical 

 nature, if it is really to be reckoned along with the connective-tissues. It seems to be rather a 

 tissue sui generis, belonging to the nervous system, and it is present in very small amount.] 



