242 NERVOUS SYSTEM. [sect. 117. 



mater ; a third corresponds to the posterior fissure, and others not 

 unfrequently correspond to the roots of the nerves and the attach- 

 ment of the ligamentum denticulatum. All these vessels, without 

 becoming narrower to any considerable degree, penetrate into the 

 grey substance, and then form their terminal expansions. There 

 are beautiful parallel vessels in the grey substance of the cerebel- 

 lum, and also, but less distinct in the cerebrum and other parts, 

 with the exception of the thalamus. The structure of the vessels 

 is, in general, the same as in other parts, still the external coat or 

 adventitia of the arteries is soon converted into a simple homo- 

 geneous envelope, and the veins have mostly not a trace of muscular 

 fibres in their walls. Beside these vessels, the brain, like the 

 cord, as Virchotv perhaps correctly supposes, appears to contain a 

 homogeneous matrix of connective tissue, which supports the nervous 

 elements. 



In the cerebral ventricles, there exists an extremely small quan- 

 tity of a serous fluid, which is obviously secreted by the vascular 

 plexuses. A second fluid, the liquor cerebro-spinalis, is contained 

 in the above- described sub-arachnoid spaces, and may be readily 

 obtained from the largest of them, which extends from the base of 

 the brain to the end of the sac of the spinal dura mater. This 

 fluid is alkaline, contains 9856 water, "055 albumen and extractive 

 matter, 084 salts, especially chloride of sodium, and its chief 

 purpose appears to be to facilitate the movement of the central 

 nervous system, and to act as regulator in the different con- 

 ditions of fulness of the vascular system. 



We may here annex some observations on the pathological conditions of 

 the structures in question. The ependyma ventricidorum has frequently, 

 especially in dropsy of the ventricles and in old age, an extremely thickened 

 fibrous layer, which, as was first stated by Purkinje, constantly contains 

 round or oblong yellowish bodies, with a concentric striation resembling 

 starch-granules, and consisting, as Yircliow has discovered, of a substance 

 allied to starch and to cellulose ; being rendered blue by iodine, and 

 violet by iodine and sulphuric acid. These corpora amylacea, which are 

 obviously pathological products, frequently exist in incredible numbers in 

 the cortical substance of the brain, in the medullary substance of the cord, 

 the Jilum terminate, the retina, in the human cochlea, in the grey nucleus of 

 the cord, in the olfactory, auditory and optic nerves. There is found, farther, 

 in the plexus chorioides, in the pineal gland, occasionally in the pia mater and 

 arachnoid (also in the cord), and, although rarely, in the walls of the ven- 

 tricles, as a constant but pathological product, the so-called brain-sand 

 (acervultis cerebri). It consists of rounded, simple or mulberry-shaped, 

 dark, mostly concentrically striated globules, 0-005'" to 0-05'", and, together 

 with these, of masses of irregular form. It contains chiefly carbonate of 



