ORGANS OF THE BODY. 



601 



pia mater than this : on their surface the ill-developed connective sub- 

 stance of the ependyma appears under the epithelial covering ( 119). 



This deepest membrane of brain and spinal cord is also the most highly 

 innervated of all. The nerves here form dense plexuses, not only in the 

 course of the vessels, but also in the connective-tissue itself. According 

 to Koelliker, they even penetrate, in part, into the substance of the brain 

 along with the liner arterial twigs. The nerves supplying the pia mater 

 spring, in the first place, from the posterior roots of the spinal cord 

 (Remak) ; and, secondly, in all probability, from the cranial nerves also, 

 as well as from the carotid and vertebral plexuses' of the sympathetic. It 

 would appear also that, from the surface of the brain and spinal cord, 

 delicate filaments may likewise be given off in the opposite direction to 

 the pia mater (Bochdalelt, Lerthossek). The choroid plexus is quite desti- 

 tute of nervous supply. 



The blood-vessels of the cerebral substance have in so far an analogous 

 arrangement to those of the cord, that they form larger meshed networks 

 in the white matter than in the grey. 



The mode in which they are disposed in the cortex of the cerebellum 

 was found by Gerlach to be different in the three layers, the white, the 

 rust-coloured, and the grey. In the first is seen a loose network of vessels 

 with long meshes fitting closely to the fasciculi of the nerve-tubes. But 

 the densest capillary network is found in the rust-coloured layer. Its 

 meshes, roundish or polygonal, branch off inwards with greater rapidity, 

 but enclose, on the other hand, the larger ganglionic corpuscles of the 

 grey stratum externally. The meshes of the latter are less dense, and are 

 arranged in the direction of lines radiating from the centre of the cere- 

 bellum. The most external boundary lamina of the grey layer is quite 

 devoid of capillaries. The latter terminate here in the form of loops. 

 The larger vessels supplying the brain enter, for the most part, with the 

 processes of the pia mater, which dip in between the convolutions from 

 the surface. Here they give off regular twigs at right angles to their 

 course, which may be traced pretty far into the cortical grey matter, form- 

 ing there, by lateral subdivision, the capillary networks just mentioned. 

 Other larger branches ramify in the white substance. 



Not less delicate, and rather similar in frontal section to that of the 

 cortical 'port ion of the cerebellum, is the 

 arrangement of vessels in the olfactory 

 bulb, as seen in the rabbit, for in- 

 stance. 



Between the two olfactory lobes 

 runs a large vessel, sending off on either 

 side fine branches, with the greatest re- 

 gularity, into the grey matter, while 

 the outer aspect of the lobes is simi- 

 larly supplied by other twigs. From 

 these a dense network is formed in the 

 grey substance, with elongated meshes 

 externally, and very small round ones 

 internally. After this we then come 

 upon the large and long meshed capillary 

 net-work of the white internal layer. 



We have still left for consideration 

 the sabulous matter of the brain (fig. 564), which is found in the choroid 



Fig. 564. Concretions from the human brain : 

 1. from the pineal gland, 2. from the 

 choroid plexus ; with their envelopes of 

 connective-tissue. 



