398 SPECIAL HISTOLOGY. 



wliicli are simple excavations in it, for the conveyance of blood and 

 lined with an epithelium ; and most of which are obviously situated 

 between the periosteal lamella and the proper dura mater, thus, in their 

 position, corresponding with the plexus venosi spinales. The arachnoid 

 membrane, either of the spinal cord or of the brain, contains no proper 

 vessels [vid. Luschka, 1. c, p. 71), whilst the pia mater in both situa- 

 tions supports not only the very copious ramifications of the vessels of 

 the nervous substance itself, but is also supplied, with a tolerably rich, 

 proper capillary plexus of its own. In one portion of the pia mater, 

 viz., in the vascular plexuses, the vessels are distributed solely in the 

 membrane itself, the branches entering the nervous substance being of 

 subordinate importance. Lymphatics it is said have recently been in- 

 jected with air and quicksilver by Fohmann and Arnold, {vid. "Anat." 

 II. p. 618) both in the pia mater on the surface of the cerebrum and 

 cerebellum, as well as in the choroid plexus, but this observation appears 

 to me very much to demand confirmation. 



The membranes of the central nervous system, also contain nerves, at 

 all events in part. In the dura mater of the cerebrum they run in the 

 periosteal lamella of the membrane, following pretty nearly the course 

 of the meningeal arteries, and are especially distinct on the a. meningea 

 media, which is accompained, not only by twigs of the nervi molles, but 

 also by a special nerve first noticed by Arnold {n. spinosus, Luschka), 

 which, according to Luschka, is derived from the third branch of the 

 n. trigeminus, the former of which are distributed with the vessels, and 

 the latter appears to be destined principally for the bones. Besides 

 these, Purkinje has noticed nerves on the anterior and posterior menin- 

 geal arteries, and Arnold long ago described the well-known n. tentorii 

 cerebelli, proceeding from the fifth pair, Avhich, as has been lately shown, 

 particularly by Pappenheim and Luschka (1. c), goes to the larger 

 sinuses of the dura mater. The elements of this white-looking nerve 

 and of the n. spinosus of Luschka, are those of the n. trigeminus, those 

 of the others, fine fibres, and in both situations they present divisions. 

 In the dura mater of the spinal cord, I, as well as Purkinje, have been 

 unable to detect any nerves ; they occur, however, as has been already 

 mentioned, in the periosteum of the vertebral canal, and on the arteries 

 going to the vertebrjB and cord, as well as in the sinuses and lax adipose 

 tissue of the canal (Luschka, 1. c). 



In the aracJiJioid itself I have never noticed any nerves, but on the 

 vessels by which it is penetrated, and in the processes connecting it with 

 the pia mater, they may perhaps be seen, especially at the base of the 

 brain — to which nerves, those seen by Luschka (Serose Iliiute, p. 70), 

 notwithstanding the divisions observed in them, appear to me to belong. 

 Bochdalek (1. i. c.) has lately described nerves of the cerebral arachnoid, 



