672 
is lined by the pia mater. We notice here a 
large interval between the arachnoid and pia 
mater, in which a considerable accumulation 
of the cerebro-spinal fluid takes place, com- 
municating with the anterior conflux of that 
fluid. In this space runs the middle artery of 
the brain, giving off its branches to the sides 
and floor of the fissure. When the convolu- 
tions which bound the fissure are separated, 
a variable number of small convolutions is 
found, projected from its floor as an insulated 
lobe, which is enclosed by a bifurcation of the 
fissure. This lobe constitutes the island (insed ) 
of Reil. 
The middle segment which lies immediately 
behind the Sylvian fissure, is on a plane much 
lower than the anterior, and corresponds on 
either side to the deep and hollow median 
A, anterior lobe; B, middle lobe ; C, posterior lobe; D, cerebellum ; a, olfactory nerves; b, 
nerves; €, third pair of nerves; d, fourth pair of ditto; e, fifth pair—portio major; é, fifth 
ninor g, seventh pair; A, filaments of origin of the glosso-pharynge 
vagus ; #, spinal accessory nerve, k, ninth nerve; I, pituitary body and process proceedi 
tuber cineream; m, mamillary bodies; n, pons Varolii; 0, medulla oblongata, 
portio minor ; fi sixth pair ; 
NERVOUS SYSTEM. (Nervous Centres. Tur Encepiaton.) 
Base of encephalon viewed from below. 
fossa of the cranium. It consists of two la- 
teral very convex lobes, commonly known 
as the middle lobes of the brain, which an 
separated from each other by a deep depres- — 
sion. These lobes, which are very accu 
limited in front by the fissure, have no e 
boundary behind, but pass off very gradually 
into the posterior lobes of the hemispheres, 
as may be seen by raising up the cerebellum. 
The transition from the middle to the pos- 
terior lobe of the hemisphere is only indicate 
by the different character of the inferior sui 
of the hemisphere, the former being convex, 
the latter concave. The subdivision, indee¢ 
of the cerebral hemisphere into middle and 
posterior lobes is purely conventional, and I 
agree with Cruveilhier that it ought to be dis- 
carded, for it has no foundation in the anatomy 
= QYy) 
