272 ANATOMY OF THE RABBIT. 
lateral wall of the skull on both sides. The chief part of the 
operation consists in removing the temporal portion of the skull 
by successive steps, exposing first the flocculus of the cerebellum, 
a small stalked body which is almost completely enclosed by the 
dorsal portion of the petrosal. The entire petrotympanic bone 
is easily detached, and if removed en masse the paraflocculus and 
probably also the roots of the facial and acoustic nerves will be 
destroyed. 
The arches of the first three or four cervical vertebrae should be 
removed, unless the anterior portion of the cord has been exposed 
in the previous dissection. 
The spinal cord may be divided at about the level of the third 
vertebra. The brain should then be raised very gently from the 
ventral wall of the skull and the nerve roots divided with a small 
sharp knife or with fine scissors. This operation requires con- 
siderable care, since the nerves are strongly attached at their points 
of exit trom the cranial wall, but very lightly attached to the brain, 
so that they are in danger of being torn away. 
The anterior end of the brain may be freed by cutting across the 
small anterior expansions formed by the olfactory bulbs. 
Portions of the dura mater removed with the brain may be cut 
away with scissors. It is adherent chiefly along two lines: one 
representing the longitudinal fissure between the cerebral hemi- 
spheres, the other the tentorium cerebelli. These parts contain the 
superior sagittal and transverse venous sinuses. 
On the ventral surface of the brain as removed appear the 
basilar and internal carotid arteries and their branches. These 
vessels should be kept intact for examination at a later stage. 
For the primary divisions of the brain see p. 71. 
4) The superficial features may be identified as follows: 
IN THE PROSENCEPHALON: 
(a) The greatly enlarged cerebral hemisphere (hemisphaerium 
cerebri) forms with its fellow of the opposite side the largest 
portion of the brain. The two structures are separated by 
the longitudinal cerebral fissure, but are connected with 
one another by the commissures indicated below. 
(b) The olfactory bulb (bulbus olfactorius) is a small ex- 
pansion lying at the anterior end of each hemisphere. Its 
