582 MANUAL OF HISTOLOGY. 



we see the substantia gelatinosa of Roland traversed in its whole circum- 

 ference by separate fasciculi of very delicate fibres, which advance later 

 into the base of the posterior cornu in part, or, taking another direction, 

 enter the pillars of Clarke. Other bands of fibres may be observed to 

 pass forwards through the latter, disappearing eventually in the grey 

 matter beyond. Others, again, are said to enter the posterior commis- 

 sure, and many, probably, the grey matter of the anterior. 



So far, then, it appears at least possible, that all the fibres of the 

 posterior root penetrate into the grey matter. And in that they here 

 probably pass between sensory ganglion corpuscles, we might expect a 

 (direct or indirect) connection with the latter. An immediate turning in 

 of a portion of the posterior root into the posterior column in order to 

 pursue a course towards the brain (" sensory fibres" of Schroder van der 

 Kolk) appears for many reasons very unlikely. 



According to Deiters the three white columns mainly composed of 

 the conducting portions of the cord may be regarded as springing from 

 the grey matter, and the system of the ganglion cells as interpolated 

 between them and the roots of the spinal nerves. 



Accepting this as correct, the ganglionic cell system would appear to 

 possess the significance of a provisional central point, from which the 

 neural tract, altered in direction, and in all likelihood simplified, takes 

 its course onward to the cerebrum. It must, however, be designated as a 

 mere point of histological dogma if all the fibres of the roots be stated to 

 have such a connection with ganglionic corpuscles. Whether the very 

 fine protoplasm processes of the latter, discovered by Deiters, are commis- 

 sures between the ganglionic cells ; whether after further isolation, and 

 increase in breadth, they become the axis cylinders of the nerves of the 

 white column's ; whether for the formation of one of the latter axial 

 structures, several of these very delicate fibrillae first combine, or whether, 

 as Gerlach maintains, the latter form a network of filaments of the most 

 extreme tenuity, are all questions to which science is unable at present to 

 give satisfactory answers/ The same want of facts is felt in regard to the 

 existence of a connection between motor and sensitive cells. 



It is generally supposed that the anterior columns serve as conductors be- 

 tween the motor nerves and the brain, and the posterior between the latter 

 and the sensory nerves, while the lateral cords partake of the nature of both. 



We shall now conclude this extremely unsatisfactory description with 

 a brief mention of the two transverse commissures of the spinal cord. 



If we examine the most anterior of these bands (/) closely, we shall 

 soon convince ourselves that a number of genuine nerve fibres exist in it, 

 enclosed in sustentacular connective-tissue, and intersecting each other at 

 various angles. In the medulla spinalis of the calf and ox, in which the 

 relations of parts may be very clearly seen (Deiters), the transverse inter- 

 secting bundles advance even into the white substance of the anterior 

 column. They arise in the grey matter on one side, and after descending 

 and again ascending to a certain extent in their course, arrive in the 

 fibrous substance of the anterior column on the opposite side. No con- 

 nection with ganglion cells can be demonstrated with certainty. Many 

 have argued from this a total decussation of the motor nervous tracts in 

 the spinal cord ; but, perhaps, without sufficient grounds. At certain 

 points, also, in the grey portion of the anterior commissure, fine nerve fibres 

 may be observed to pass across from one side of the cord to the other. 



In the posterior commissure (h), likewise, we have a connective-tissue 



