THE NERVOUS SYSTEM. L59 



the gritty matter of the brain (brain-sand). It consists of 

 roundish, simple or mulberry-shaped, opaque, mostly con- 

 centrically striated globules of 0-005 — 0*05'", and together 

 with them of angular bodies, of a stalactitic, clavatc, or other 

 irregular figure, with an uneven, botryoidal, scaly surface; and 

 also in the form of simple, cylindrical, rigid fibres, either 

 branched or reticular, and of fine particles. The brain-sand 

 contains principally carbonate of lime, but also phosphate of 

 lime and magnesia, and an organic substance, which after the 

 salts have been removed, for the most part perfectly retains 

 the figure of the concretion, that is to say, of a concentrically 

 laminated pale body, or as clear fibres. It is quite certain that 

 this brain-sand, when it assumes the form of elongated, 

 branched, reticular bodies, is simply developed in the bundles 

 of connective tissue (fig. 153), as, not unfrequently, in the 

 pineal gland and in the membranes of the brain; in other 

 cases it appears to be an independent incrustation on fibrinous 

 concretions. Whilst cells impregnated with calcareous matter, 

 which Remak ('Obs./ p. 26) supposed them to be, accord- 

 ing to Harless (Mull. 'Arch./ 1845, p. 354), do not exist. 

 Lastly, also, may be mentioned the Pacchionian granula- 

 tions of the pia mater, and ossifications of the membranes. 

 The former, which are situated principally on both sides 

 of the faLv major, on the flocculi, in the choroid plexuses, &c. 

 consist chiefly of a tough fibrous substance, not unlike imma- 

 ture connective tissue, containing also undeveloped elastic 

 tissue, and corpuscula amylacea. The latter, which are true 

 osseous plates, occur sometimes on the inner surface of the 

 cerebral dura mater, sometimes on the arachnoid, particularly 

 of the cauda equina.'] 



PERIPHERAL NERVOUS SYSTEM. 



§ 119. 



Spinal nerves. — The thirty-one pairs of nerves springing 

 from the spinal cord, arise, with few exceptions, hy anterior 

 and posterior roots. Receiving a delicate tunic from the pia 

 mater, they converge, and are continued across the subarach- 

 noid space, to perforate, independently of each other, the 



