220 TWENTY-FIRST LECTURE. 



Our supporting substance comes forward most purely in 

 the vicinity of the axis canal ; externally, toward the periph- 

 ery of the gray substance, it becomes profusely permeated 

 by nervous elements. It has been given the name of the 

 neuroglia (Virchow). 



As we here naturally pass over the subordinate varieties, 

 we will characterize this supporting tissue as a very delicate 



and extremely decomposable, fine reti- 

 cular substance, with nuclei at the 

 nodal points, so that cell-bodies must 

 be present here (Fig. 188). The fine 

 clefts are permeated by a chaotic maze 

 of the finest nerve fibrillar ; in the larger 



Fig. 188.— Neuroglia from the Spa ceS are ganglion Cells, 

 gray substance of the human cen- l o o 



trai nervous system (cerebellum), Proceeding; further towards the peri- 



with embedded nuclei. <-> '■ 



phery of the spinal cord, we arrive at 

 the white columnar systems, and here the connective-tissue 

 substratum has become more compact and firmer. Some- 

 times appearing more homogeneous, sometimes more striated, 

 and again containing nuclei in individual nodal points, it 

 forms a system of septa, an incomplete one it is true, which 

 surrounds the descending nerve fibres as a fenestrated system 

 of sheaths (Fig. 170). Thicker, connective-tissue vascular 

 lamellae radiate out to the pia mater which, as is known, sur- 

 rounds the surface of the spinal cord. This envelope finally 

 sends folds with considerable blood-vessels into the anterior 

 and posterior longitudinal clefts of the organ. 



The vascular net- works of the white substance, which main- 

 tain a radial arrangement, are scanty and large-meshed. The 

 capillary net-work of the gray substance is compact and 

 narrow-meshed ; the latter is very vascular. 



Let us now consider the nervous contents of the connective- 

 tissue frame-work. 



The white cortical substance consists essentially of vertically 

 arranged nerve tubes of 0.0029 up to 0.009 nim. diameter. 

 The thickest fibres are presented by the anterior columns ; 

 the finest by the posterior, especially towards the fissura pos- 



