114 ANTHROPOLOGY. 
The posterior segment, as occupying the posterior fossa of the cranium, is 
on a level considerably below that of the middle segment. A part worthy 
of especial notice is the pons Varoliz, which is situated immediately behind 
the interpeduncular space, the crura cerebri appearing to emerge just above 
its anterior border. From its posterior edge the medulla oblongata extends 
downwards and a little backwards, occupying a notch or depression between 
the lobes of the cerebellum. The fibres of the pons are seen passing out- 
wards and backwards into each hemisphere of the cerebellum, ire the 
inferior layer of each crus cerebelli. 
2. DISSECTION OF THE ENCEPHALON. If we makea horizontal section 
of one hemisphere, nearly on a level with the corpus callosum, we shall per- 
celve what is known as the centrum minus ovale, a mass of white fibrous 
substance surrounded by an irregularly undulating line of grey; a second 
horizontal section passing through both hemispheres on a level with the 
corpus callosum presents the centrum magnum ovale, a line of grey sub- 
stances surrounding the central mass of white. The corpus callosum, or 
superior cerebral commissure, will now be seen in the middle line of the 
cerebrum, between three and four inches long, marked by two or three 
raised longitudinal Hines nearly parallel to each other (the raphe); from 
these, several transverse lines pass to either side. The posterior end of the 
corpus callosum is bent downwards above the transverse fissure, and is con- 
tinuous with the fornix and hippocampi; anteriorly it is continued into the 
anterior lobes: in the middle it joins the tuber cinereum and the optic com- 
missure. It connects the white fibrous substance of both hemispheres, and 
covers like an arch the lateral ventricles, the septum lucidum, and the 
fornix. 
On dividing the corpus callosum at a little distance from either side of 
the raphe, the lateral ventricles or cavities of the brain will be opened, one 
on each side, and separated by the septum lucidum. This consists of four 
laminez on each side: 1. The lning membrane of the ventricle; 2. A 
thin grey layer; 3. A compact white fibrous layer; 4. A delicate mem- 
brane which lines the small cavity existing in it, and termed the /ijth 
ventricle. 
The lateral ventricles extend from the middle of the brain into the 
anterior and posterior lobes, also into the inferior part of the middle lobe; 
each has, therefore, three cornua. The anterior cornu is bounded superiorly 
and laterally by the corpus callosum, and inferiorly by the large extremity 
of the corpus striatum. ‘T'he middle or body of each ventricle is bounded 
superiorly and externally by the corpus callosum; internally by the septum 
lucidum, and inferiorly by the posterior extremity of the corpus striatum, 
the lamina cornea, the tenia semicircularis, the optic thalamus, the choroid 
plexus, and the fornix. The posterior cornu is bounded superiorly and 
laterally by white substance, and inferiorly by the hippocampus minor. 
The inferior cornu is bounded superiorly by the optic thalamus and corpus 
striatum ; inferiorly by the hippocampus major and corpus fimbriatum or 
teenia hippocampi, over which the choroid plexus is folded. 
In making a brief individual reference to the different bodies observed in 
820 
