8 INTRODUCTION. 



termination of the medulla oblongata, consists of two substances, form- 

 ing, together, a soft compressible mass ; these substances are regularly 

 disposed, but their distinct physiological influence and properties yet 

 remain to be discovered : the one is termed the cineritious or cortical, the 

 other the medullary substance. The cineritious or cortical substance is of 

 a greyish colour, soft, and appears to the eye to be of an homogeneous 

 composition : it is, however, permeated by minute blood vessels, the 

 presence of which may be demonstrated by means of coloured injections. 



The medullary substance is firmer in its texture than the cineritious ; 

 of a white colour, and perfectly opaque : it consists, as is discernible by 

 means of a lens, of fibres disposed in different directions ; and it would 

 appear to be comparatively destitute of blood vessels, or to have them of 

 extraordinary minuteness, as coloured injections do not penetrate through- 

 out the whole of its parts. In the brain, exclusively so called, the cine- 

 ritious matter invests the medullary substance, which latter constitutes the 

 mass of the interior : in the medulla oblongata, on the contrary, the cine- 

 ritious matter is posited in the interior. Chemistry throws but little 

 light on animal physiology, or the vital properties of organs, in living 

 bodies : to learn, therefore, that the brain, as analyzed by Vauquelin, 

 consists of water, fatty matter, white, and reddish ; of albumen, 

 osmasome, phosphorus, acids, salts, and sulphur or that, in the cineri- 

 tious matter, Professor John detected muriate of soda, a sulphate, the 

 phosphates of lime, soda, ammonia, and magnesia, with a trace of the 

 phosphate of iron, and silica, is but of trifling importance. The brain, 

 then, thus constituted of a cineritious and a medullary substance, is 

 divided into several parts, and covered with certain membranes for its 

 better protection : of these, the first is the dura mater, which lines 

 the skull ; it forms also various processes, or expanded sheets, which 

 divide between or support the different parts of the brain ; and it forms, 

 moreover, between its folds, large tortuous canals, or sinuses, for the 

 reception of the venous blood : it is of a tough and fibrous tissue, and 

 is closely connected with the internal table of the cranial bones, by means 

 of numerous blood vessels. Beneath the dura mater is a more delicate 

 membrane, beautifully transparent, enveloping the brain, but without dip- 

 ping into its convolutions : it is termed, from its fineness, the arachnoid 

 membrane (membrana arachnoidea). 



The third membrane is the real investment of the brain : it is termed the 

 pia mater, and is of exceeding thinness and vascularity, exhibiting numer- 

 ous blood vessels, which are beautifully distributed over it, and which 

 pass from it into the cineritious substance of the brain itself. Instead of 

 simply investing the brain, it follows all its convolutions and inflections, 

 and lines its different cavities. 



The brain, considered as a whole, when fully developed, consists of 



