STRUCTURE OF THE WHITE COLUMNS OF THE SPINAL CORD. 333 



In the immediate vicinity of the connective-tissue spaces, 

 however, the microscopical characters of the tissue undergo 

 alteration : the fibrillse are no longer visible ; in their stead, an 

 extremely finely granular substance makes its appearance, 

 which is directly continuous with the fibrillated tissue, and is 

 prolonged into the areas of the trabecular plexus, so completely 

 filling them that only room is left for the chiefly vertically 

 ascending nerve fibres a relation that is most beautifully 

 visible in thin transverse sections. In such sections the trans- 

 versely divided nerve fibres appear immediately surrounded by 

 this finely granular substance, together with not unfrequently, 

 in certain spots, round holes, from which the sections of the 

 nerve fibres have fallen out (fig. 219, B c). This finely granu- 

 lar substance is traversed in all directions by extraordinarily 

 fine fibres which unite with each other into a plexus by 

 extremely numerous communicating branches (fig. 219, A a). 

 The microscopic structure of the finely granular substance, and 

 the plexus of extremely fine fibres contained in it, only 

 distinctly visible in the very thinnest sections, presents the 

 closest similarity to the matrix of certain yellow or retiform 

 cartilages, as, for example, the arytenoid cartilage of the Ox. 

 Opinions are divided in regard to the histological value of this 

 plexus of extremely fine fibres. Kolliker* considers it to be a 

 plexus of stellate cells, which however are peculiar in that their 

 processes undergo frequent subdivision, and communicate very 

 freely, not only with each other, but with those of other and 

 adjoining cells. Henle and Merkelf refer indeed to the simi- 

 larity of this fibrous plexus to the fibrillation of fine elastic 

 lamellse, but classify the fibres with those of connective tissue, 

 both on account of their size and their refractive powers in 

 regard to light, as well as for their chemical reactions. I am 

 unable to adopt either of these views, but regard the fibrous 

 plexus as belonging to elastic tissue, first on account of the re- 

 markable resemblance it presents to certain elastic or retiform 

 cartilages, and secondly because these fibres, like those of elastic 

 tissue, resist for a considerable period the action of alkalies. 



* Ha/ndbuch der Gewebelehre, 5th edition, p. 267. 



t Zeitschrift fur rationelle Medicin, 3 R., Band xxiv., p. 56. 



