402 CLASSIFICATION OF NERVES. 



cells embedded in a soft granular matter, which serves as a bond of 

 connection between them. The cells vary in size from x ^ to 

 3^ of an inch in diameter; they are of a reddish grey colour, 

 and are composed of a moderately thick capsule, containing a soft 

 granular pulp and a nucleolated nucleus adherent to the inner surface 

 of the investing capsule. The contents of the nucleus are similar to 

 those of the parent cell, and the nucleolus may be either single or 

 granular. Besides the constituents of the nerve-cell, there are pig- 

 ment granules in variable number, sometimes dispersed generally 

 through the pulp, and sometimes collected into small clusters, and 

 giving to the cell a various tint of grey. It is to these pigment- 

 bearing cells, collected together in greater or smaller numbers, that 

 different parts of the brain owe their relative degrees of intensity of 

 grey. The general form of the nerve-cells is globular, but there are 

 found mingled with the globular cells others of different shape. 

 Some of these latter are oval, oblong, or flattened, but the most re- 

 markable form is that which is termed caudate, from its sending off 

 from its periphery one or more cogcal processes of variable length. 

 From the capsules of the nerve-cells filaments are frequently given off, 

 which serve to connect the cells together, and the number and 

 arrangement of the cells offer many peculiarities in different parts of 

 the cerebro-spinal mass. 



Two kinds of grey substance are described by Rolando as existing 

 in the spinal cord ; the one (substantia cinerea spongiosa vasculosa) is 

 the ordinary grey matter of the cord, and the other (substantia cinerea 

 gelatinosa) forms part of the posterior cornua. The former resembles 

 in structure the grey matter of the brain, while the latter is composed 

 of small bodies resembling the blood corpuscles of the frog. 



The nerves are divisible into two great classes ; those which pro- 

 ceed directly from the cerebro-spinal axis, the cranial and spinal nerves, 

 and constitute the system of animal life ; and those which originate 

 from a system of nervous centres, independent of the cerebro-spinal 

 axis, but closely associated with that centre by numerous communica- 

 tions, the sympathetic system, or system of organic life. 



The division of nerves into cranial and spinal is purely arbitrary, 

 and depends upon the circumstance of the former passing through the 

 foramina of the cranium, and the latter through those of the verte- 

 bral column. With respect to origin, all the cranial nerves, with the 

 exception of the first, olfactory, proceed from the spinal cord, or 

 from its immediate prolongation into the brain. The spinal nerves 

 arise by two roots ; anterior, which proceeds from the anterior segment 



envelope, and a contained substance, neurine. 4. A nerve-cell, shewing its 

 composition of a granular-looking capsule and granular contents. 5. Its nu- 

 cleus containing a nucleolus. 6. A nerve-cell from which several caudate pro- 

 cesses are given off. It contains, like the preceding, a nucleolated nucleus. 7- 

 The third constituent of the medullary masses, namely, granules, or rather 

 minute cells. These are dispersed among the cerebral fibres in great numbers ; 

 they present every variety of size, and are many of them nucleated. 



