el 
NERVOUS CENTRES. (Human Anatomy. Tus Encepnatoy.) 
radiate extensively. It may be stated to con- 
nect the convolutions of the middle lobes and 
the corpora striata. 
3. The posterior commissure is a band of 
fibres, extended between the posterior extre- 
mities of the optic thalami, upon which rests 
the base of the pineal body. Those fibres, 
which immediately support that body, have 
been distinguished as the pineal commissure ; 
but as they are evidently part of the same 
system as those which constitute the posterior 
commissure, there seems no good reason for 
separating them. 
4. The soft commissure is also extended be- 
tween the thalami. It is composed of vesi- 
cular matter with fibres, which pass from 
one side to the other. The intermixture 
of its fibres with vesicular matter distin- 
guishes it from the other transverse commis- 
sures already described. A layer of a simi- 
lar nature connects the locus niger of each 
crus cerebri, and fills up the space between 
the crura—interpeduncular space. This has 
_ been already described as the pons Turini, 
posterior perforated space. 
It consists of 
fibrous matter intermixed with vesicular, ex- 
tended between the crura cerebri. It seems 
analogous to the soft commissure, and there- 
fore entitled to be regarded as a commissure. 
Of the manner in which the commissures 
connect the various parts between which they 
are placed, it is difficult to form an exact 
opinion. It is most probable that they form 
an intimate union with the grey matter of the 
Segments which they serve to connect. It 
might also be conjectured that they are conti- 
‘nuous with some of the fibres of the segments 
which they unite, or that they interlace with 
them in some intricate way, so as to come into 
intimate or frequent contact with them. 
Tuber cinereum.—At the base of the brain 
we have already described a layer of pale grey 
matter which fills up the interval between the 
mamillary bodies and the optic commissure. 
It extends above the optic commissure for- 
_ wards to the anterior reflexion of the corpus 
callosum, and forms intimate connections with 
the anterior pillars of the fornix, the optic 
tracts, the septum lucidum, and at the floor 
of the third ventricle with the optic thalami. 
It consists of vesicular matter with fibres, and 
resembles very much the soft commissure, to 
which it is very probably analogous in office. 
The process called infundibulum or pituitary 
process extends from the inferior surface of the 
tuber cinereum down to the pituitary body. 
It is hollow, wide above, where it commu- 
nicates with the third ventricle, and narrow 
below at the pituitary body. When cut across, 
fluid will escape from the third ventricle 
through it, and a probe passes readily from 
that cavity into it. It is composed of a layer 
of granules, derived, no doubt, from the epi- 
thelial lining of the third ventricle, and some 
vesicular matter with bloodvessels and fibrous 
tissue, which latter is derived from the pia 
mater, and the special sheath of arachnoid 
reflected upon it. 
{ 
703 
Pituitary body—The process just described 
is the connecting link between the brain and 
that glandiform body, the pituitary gland or 
hypophysis. This body, situate in the sella 
Turcica, is of a rounded form, longer in the 
transverse than the antero-posterior direction, 
concave on its superior surface, into which the 
_onpevans process is inserted. It is surrounded 
y dura mater, which projects over it, leaving . 
an opening for the passage of the infundi- 
bulum. 
The pituitary body is about six lines in its 
transverse diameter and three lines from before 
backwards: its weight, including the infundi- 
bulum, is about eight grains. It consists of 
two lobes, one anterior, the other posterior. 
The former is kidney-shaped and lodges the 
latter in the notch of its posterior edge. In 
point of size the anterior lobe is nearly double 
the posterior. 
The colour of the posterior lobe is lighter 
than that of the anterior, and resembles that of 
the grey matter of the brain. 
This body is proportionally larger in early 
life than at the later periods, and it is certainly 
more developed in the lower mammalia than 
in man. It is very large in fishes, and pro- 
bably reaches its maximum of size in that class 
of animals. 
The structure of the pituitary body resem- 
bles very much the grey cerebral matter. It is 
composed of large nucleated vesicles, sur- 
rounded by a granular matrix, with bundles of 
white fibrous tissue. This fibrous tissue either 
forms an essential element in its constitution, 
or accompanies the bloodvessels which are 
found in it in great numbers. Its substance is 
soft, but not so soft as the cerebral matter, 
and when pressed between the fingers is re- 
duced to a greyish pulp, like the substance of 
an absorbent gland in an early stage of suppu- 
ration. 
Earthy concretions have been occasionally 
but very rarely found in the pituitary body. 
This circumstance, its colour, its glandiform 
character, and its extra-cerebral situation in 
connexion with the third ventricle, give it a 
certain degree of analogy to the pineal body. 
But in this latter nervous fibres have been 
found, of which I have failed to discover any 
trace in the pituitary, nor is the pituitary body 
connected to the brain by fasciculi of fibres as 
the pineal body is. The use of both is equally 
involved in obscurity; but from their con- 
stancy it may be argued that their function is 
not unimportant. It has been supposed that 
the pituitary body is a large ganglion belong- 
ing to the sympathetic system: this opinion, 
however, wants the all-important foundation of 
anatomy to rest upon, inasmuch as we find 
that the body in question is devoid of the ana- 
tomical characters of a ganglion. It-may w th 
more propriety be classed with the glards 
without efferent ducts; and from its numerous 
vessels, and its close relation to part of the 
venous system within the cranium, it may be 
connected with the process of absorption or re- 
moval of the effete particles of the brain. 
