910 



THE NERVOUS SYSTEM 



branes; (2) the arachnoid, the much less dense, web-like middle membrane; 

 and (3) the pia mater, a thin, compact membrane, closely adapted to the sm-face 

 of the central system, into which it sends numerous connective-tissue processes. 

 It is highly vascular in that it contains the rich superficial plexuses of blood- 

 vessels from which the intrinsic blood supply of the central system is derived. 

 The space between the dura mater and the arachnoid is known as the sub-dural 



Fig. i716. — Dorsal Aspect of the Medulla Oblongata and Spinal Cord with the Dura 

 Mater Partially Removed. (Hirschfeld and Leveille.) 

 A B 



Superior peduncle 

 of the cerebellum 

 Median sulcus oi 



4th ventricle 

 Glosso-pharyngeus 

 Vagus 



Spinal accessory 



Ligamentum 

 denticulatum 



Posterior median 

 sulcus 



A ventral root 

 A dorsal root 



XII. 



L 1 — 



S.I. 



Spinal 

 ganglion 



cavity, and that between the arachnoid and the pia mater is the sub-arachnoid 

 cavity. 



The Duea Mater 



In the fresh condition the dura mater appears as a bluish-white, exceedingly 

 resistant membrane, forming the outermost envelope of the entire central nervous 

 system. Its external surface or tliat next to the l)ony wall is rough, while its 

 internal surface appears smooth, due to the fact that the subdural cavity partakes 

 of th(! nature and has the lining of a lymph-space. The cranial dura mater 

 consists of two distinct, closely associated layers, the outermost of which serves 

 as the internal jxTiosteum of the cranial bones. The spinal dura mater is 

 described as consisting of but one layer, '{'he internal periosteum of the spinal 



