Bauhaus-Universität Weimar

Titel:
The Cyclopaedia of Anatomy and Physiology, vol. 3: Ins-Pla
Person:
Todd, Robert Bentley
PURL:
https://digitalesammlungen.uni-weimar.de/viewer/image/lit29464/686/
678 NERVOUS SYSTEM. (Nervous Centres. The Encephalon.) 
The interval between the processus cerebelli 
ad testes is occupied by a horizontal stratum of 
nervous matter composed of a thin layer of grey 
and of white matter. This is called the valve of 
Vieussens, although there is evidently nothing 
valvular in its nature or office. Its surface is 
marked by slight transverse depressions and 
eminences. The median lobe of the cerebel¬ 
lum overlaps and conceals it from view. 
The valve of Vieussens* must be regarded 
as a portion of the median lobe of the cerebel¬ 
lum, which is extended forwards between the 
processus cerebelli ad testes. Its constitu¬ 
tion is precisely the same as the laminæ ofthat 
body, and the transverse markings upon its 
superior surface are indications of imperfectly 
developed fissures between the laminae. 
The corpora quadrigemina form the anterior 
superior part of the mesocephale. They lie above 
the crura cerebri, upon those columns of nervous 
matter by which the latter bodies are connected 
with the medulla oblongata. These columns 
are continuous above with the optic thalami, 
and below with the central portion of the me¬ 
dulla oblongata, the olivary tracts, ox fasciculi 
innominati of Cruveilhier. They are distin¬ 
guished by their reddish grey colour and their 
close resemblance in point of structure to the 
optic thalami. In transverse section they appear 
as two columns, circular in outline, quite dis¬ 
tinct from the surrounding greyish matter in 
which they seem imbedded (fig- 388, i). 
The lower half of the thickness of the me¬ 
socephale is formed by transverse curved fibres 
with anterior convexity, which extend between 
the lateral lobes of the cerebellum, and of 
longitudinal fibres which interlace with the 
superior layers of those transverse fibres and cross 
them at right angles. The former constitute 
the pons Varolii, a great commissure between 
the hemispheres of the cerebellum ; the latter 
are, in greater part at least, the fibres of the 
anterior pyramids of the medulla oblongata, 
which ascend through the pons, and enter into 
the formation of the inferior layer of each crus 
cerebri. 
In examining the inferior surface of the me¬ 
socephale, the pons Varolii, we observe that a 
longitudinal groove extends along its middle 
from above downwards. In this lies the ba¬ 
silar artery. Above the anterior edge of the 
pons, the crura cerebri are seen emerging, and 
diverging from each other as they pass, to enter, 
stalk-like, into the inferior surface of the cere¬ 
bral hemispheres. Beneath its posterior edge, 
the medulla oblongata is seen, its anterior and 
* Valimla cerebri major is the name which Yi- 
eussens applied to this process. He describes it as 
“ membrana quam transversus medullaris tractus 
circa anteriora subit, processui vermiformi anteriori, 
processibus a cerebello ad testes et posticae pontis 
Varolii parti adhæret etunitur.” He further adds, 
“ ill am valvulæ vices gerere asserimus. Ex quo fit, 
ut habita officii et magnitudinis illius ratione, 
ipsam valvulam cerebri majorent nominemus, ut 
earn a membranaceis ligamentis distinguamus, quæ 
intra longitudinalis et lateralium sinuum cavitates 
valvularum minorum vices supplent et munia præ- 
stant.”—Neurographia Universalis, p. 76. Ed. Lugd. 
1716. 
middle columns passing through the mesoce- \ 
phale to the crura cerebri. On each side the 
fibres of the pons pass off into each hemi¬ 
sphere of the cerebellum and form the inferior 
lamina of each crus of that organ. 
The cerebellum.—Some account of the ge- :j 
neral disposition of the cerebellum will serve ; 
to conclude this brief review of the topography 
of the brain. The superior surface of this 
organ is a little above the level of the qua¬ 
drigeminal bodies. It is smooth and slightly 
convex. The lamellæ of the cerebellum are 
visible upon it, but cannot be separated with¬ 
out removing the arachnoid and pia mater. 
A notch is seen, dividing the posterior edge 
into two equal portions, and a larger notch 
exists in front, at which the cerebellum forms 
its connection with the mesocephale. These 
notches denote a subdivision of the organ into 
two lateral portions, or hemispheres, and a me¬ 
dian portion. The superior surface of the 
median portion is called the superior ver¬ 
miform process; its anterior terminal laminæ 
form the valve of Vieussens. On the inferior j 
surface the hemispheres of the cerebellum are : 
much more convex than on the superior. The : 
median portion too is somewhat differently 
arranged on its inferior surface ; it consists of a \ 
series of laminæ, following a transverse direc- • 
tion ; those in its centre are of greater trans- • 
verse extent than those at either extremity, >, 
whence the appearance of a crucial figure re- • 
suits. This is the inferior vermiform process. 
The posterior margin of the cerebellum is ! 
convex, and corresponds to the concave surface: : 
of the occipital bone, the falx cerebelli occupy--]? 
ing the notch in its middle. Along the line of I 
this margin, the pia mater sinks into a deep: j 
fissure, which takes a horizontal direction from i 
behind forwards, and divides the cerebellum i 
into a superior and inferior portion. 
As the brain, removed from the cranium,,;: 
lies with its base upwards, the medulla ob-- 
longata is seen between the lateral hemispheres^ 
of the cerebellum occupying a portion of thei 
depression between them, in which is the in-i 
ferior vermiform process (fig. 382). j 
The fourth ventricle is a lozenge-shapedll! 
cavity situated in the upper and posterior parte, 
of the medulla oblongata, and formed by thei 
separation of its postero-lateral columns (cor-' 
pora restiformiu). The cerebellum contributes’: 
to inclose it above by means of the anterior? 
laminæ of the superior vermiform process and? 
the valve of Vieussens, and below and behind? 
by the inferior vermiform process (fig. 386). 
We now proceed to the examination of thee? 
various segments of the encephalon, with a 
more special reference to the structure ana 
physiological bearing of each. It may be hem 
remarked that, while all the segments are mt 
timately connected with each other and ar«j 
therefore mutually dependent, there is mucll 
in their structure to justify the assumption thaï 
each is capable of exercising an independent 
function, which is, however, liable to be mot 
dified by the influence which any one, or all o 
the other segments may have upon it. 
Of the medulla oblongata. (Fr. moeltif
        

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