76 
MAMMALIAN ANATOMY 
out by carefully removing the arachnoid, pia mater, and blood 
vessels which fill them. The most conspicuous of these upon the 
dorsal surface is the central sulcus of Rolando, which is at right 
angles to the longitudinal fissure and partly separates frontal from 
parietal lobes; the upper end of the lateral cerebral fissure (fissure 
of Sylvius), mainly latero-ventral in location, which partly 
separates frontal from temporal lobes may also be seen. Note 
the general direction and arrangement of gyri and sulci in each 
area thus mapped out, and determine to what extent this 
corresponds to the arrangement in the human brain (cf. 
reference books). 
By gently removing the arachnoid from the longitudinal 
fissure, and pressing the cerebral hemispheres apart, the white 
surface of the corpus callosum may be seen extending across the 
midline between the two hemispheres. Posterior to this is located 
the small median outpushing of the roof of the diencephalon, 
the pineal body (epiphysis), the disclosure of which is made 
possible by the removal of the arachnoid from the transverse 
fissure. This allows the cerebellum to be bent gently backward 
thus making it possible to see also the four rounded eminences, or 
corpora quadrigemina, which form the dorsal portion of the 
mesencephalon. The pineal body lies in the depression between 
these and the cerebral hemispheres. 
Lateral Aspect. —Note the deep lateral cerebral fissure which 
crosses the lateral surface of the hemisphere vertically, thus form¬ 
ing the boundary between the frontal and the temporal lobes, while 
the supramarginal and angular gyri of the inferior parietal lobe 
arch about its upper end. By gently pressing forward the 
anterior wall of the lateral fissure, which is known as the oper¬ 
culum, it is possible to disclose at the bottom of the fissure a deep 
region of the convoluted surface of the cerebrum known as the 
insula, which will, however, be more plainly seen in the subsequent 
dissection. At its lower end the lateral fissure meets at right 
angles the rhinal fissure, which extends longitudinally the whole 
length of the cerebral hemisphere and may be better studied from 
the ventral aspect. 
Ventral Aspect. —Note the conspicuous rhinal fissure which 
crosses at right angles the ventral end of the lateral fissure, and 
