456 



SPECIAL HISTOLOGY. 



interims, plexus vertebralis), the cerebral nerves may par- 

 ticipate in the supplying of the pia mater, since Bochdalek 

 has noticed numerous fine twigs, given off from the roots of 

 many of the cerebral nerves, of the same structure as the roots 

 themselves, joining the nervous plexuses of the arteries at the 

 base of the brain and of the pia mater of that region, and of 

 the cerebellum, as well as in the plexus chorioideus ventric. 

 quart. (?). He also found that isolated fine filaments entered the 

 jria mater, directly from the medulla oblongata, the pons Varolii, 

 and crura cerebri, which were not previously conjoined with the 

 neighbouring nervous trunks. 



B. Vessels of the central nervous system. — AVith respect to 

 the distribution and condition of the blood-vessels — the brain 

 and spinal cord agree almost entirely. After ramifying to a 

 considerable extent in the pia mater, the arteries enter the 

 nervous substance, except in a few situations (substantia per- 

 forata, pons), as fine, though 

 still distinct, arterial vessels, 

 and ultimately subdivide, by 

 continuous ramification, for the 

 most part at acute angles into 

 a rather wide network of very 

 fine capillaries, from which 

 again the venous radicles arise, 

 joining so as to form the well 

 known trunks, both on the 

 surface and in the interior (fig. 

 152). The grey substance is 

 invariably much more richly 

 supplied with vessels than the 

 white,theplexusformedbythem 

 being closer, and the capillary 

 vessels themselves of less cali- 

 bre, to which its colour is in 

 some respect due. According 

 to E. H. Weber, the interstices 

 of the capillaries in the medullary substance, measure 00142'" 

 in width and O025'" in length ; in an injected preparation by 



Fig. 152. Vessels of the cerebral substance of the Sheep, from one of Gerlach's 

 injections : a, of the grey ; b, of the white substance. 



