480 - On the Nervous Systems of 
bility. Both these substances are, very evident 
in the brain and spinal marrow: But the cine- 
ritious matter is not so easily observed in the 
nerves, being in a very small proportion to the 
medullary. Dr: Monro, however, informs us, 
that he has by an attentive examination found 
it in most of the nerves.t The relative posi- 
tion of the cineritious and medullary substances 
differs in different parts of the nervous system. 
The conszstence of the brain is softer in cold~ 
blooded animals and in some fishes is almost 
fluid. . 
+ * Although the nerves have been universally con- 
sidered as a continuation of the pure medullary substance of 
the brain and cerebellum; yet I find, on accurately ex- 
amining them, that with a few exceptions, particularly of 
the optic nerves and portio mollis of the auditory, they 
are all of a browner colour than the medullary substance, 
their pia mater. seeming to furnish a quantity of cine- 
ritious matter.”’—* The optic nerves and portio mollis of 
the auditory seem, indeed from their bright white colour, 
to receive from their pia mater little or no cineritious mat- 
ter in their progress to the eye and ear: but, as soon as 
they enter these organs to form the retina and to be 
spread out on the membrane of the cochlea and semi- 
circular canals, instead of . remaining white and opake, 
they become cineritious. The cause of which is, that, 
contrary to what has been alleged by all authors, they 
carry with them their pia mater, and from that mem- 
brane every fibre of the nerve receives Cineritious mat- 
ter.’ Observations on the Structure, Gc. of the Nervous 
System, p. 32- 
