George L. Streeter 15 



and Myelinated Axis-Cylinders, w^hich form the fibre tracts and make up 

 the bnlk of the white substance. The histology of the cord will be dis- 

 cussed under these heads. 



The neuroglia was studied in preparations stained by the iron haema- 

 toxylin picro-fuchsin method of Weigert. This method cannot be spoken 

 of as a glial stain; on the contrary, the glia does not stain with fuchsia as 

 in the original Van Grieson method, but remains a yellowish brown and 

 is seen in sharp contrast to the brilliant red connective-tissue elements. 

 By combining the original Van Gieson method and the Weigert modifi- 

 cation we may study the glial distribution by a process of exclusion ; this 

 permits the following general description : 



The glia fibres are more numerous in the grey substance than in the 

 white, and are more numerous in the ventral horns than in the dorsal 

 horns. They form an especially thick mass in the region of the central 

 canal. In the white matter on the periphery, adjoining the pia, is a 

 rather uniform layer of closely-lying fi.bres which forms a glial sheath to 

 the cord, the peripheral glia sheath. This layer, at a point corresponding 

 to Lissauer'"s fasciculus, is thickened and extends into the substance of the 

 cord as a broad strand to meet the tip of the dorsal horn, which fails to 

 reach the border of the cord. This strand spreads laterally to the dorsal 

 horn and forms the web-like formatio reticularis situated in the median 

 part of the lateral funiculus. 



In most sections another glial process is seen extending from the 

 sulcus longitudinalis dorsalis toward the central canal, the septum, longi- 

 iudinale dorsale, supporting a blood-vessel with its connective tissue 

 sheath. Aside from the peripheral sheath and the processes as mentioned, 

 the glia of the white substance forms a more or less uniform framework, 

 supporting the nervous elements proper. There remains to be mentioned 

 a special modification of the glial arrangement associated with the forma- 

 tion of the sinus rhomboideus. 



Sinus Ehomboideus. 



A macroscopic description of this structure has already been given, and 

 we have spoken of the delicate gelatinous tissue with which it is filled. 

 From the study of a series of transverse sections through this region it is 

 our conclusion that this tissue is not a new structure, but is identical with 

 the peripheral glia sheath and the septum dorsale which have become 

 modified in their histological character. 



In sections through, the 29th segment there is a marked increase in 

 the size of the sulcus longitudinalis dorsalis, which penetrates ventrally 

 one-half the length of tlie septum dorsale and splits it in wedge-shape 



