PRACTICAL DIRECTIONS. 465 
foramen of Monroe, the anterior commissure. See all these also on 
a preparation (Fig. 148). 
e. Remove the occipital and parietal portions of the cerebrum, 
on the side already dissected, so as to expose the roof of the third 
ventricle and the midbrain in your specimen, and note the pineal 
body, choroid plexus of third ventricle, and structures on the roof of 
the midbrain (Fig. 141). 
J. Remove the choroid plexus or roof of the third ventricle and 
study again the thalami (Fig. 141). 
g. Make a longitudinal section of the brain, in the following 
manner: Use a very sharp large scalpel, or a razor. . Have this wet 
with the alcohol mixture at the time of using. Place the brain 
ventral surface down on a sheet of cork or a block of soft wood, the 
long axis of the brain coinciding with the direction of grain of the 
wood. Holding the brain firmly with one hand, place the wet knife 
beween the hemispheres with its edge resting on the corpus callosum. 
See that it is in the median plane and parallel with the long axis of 
the brain. See also that it is not inclined to one side or the other, 
so that it will make on cutting a median section throughout. The 
point of the knife should just reach the cork or wood between the 
olfactory bulbs. Now draw the knife caudad, keeping its point 
against the cork: the brain will thus be divided. 
If the section is not exactly median, observe the amount of 
divergence by placing the two halves together and finding the 
median ventral line. Then on the half that has /oo much slice away 
thin shavings until the cavities are exposed, showing the section to be 
median. Compare with a demonstration section or Fig. 143. Draw 
the section and compare with a section of shark’s brain (see Fig. 143). 
A, Study a series of transverse sections, identifying parts. 
Observe especially in these sections the fornix, corpus callosum, and 
ventricles, and the distribution of white and gray matter (see Figs. 
149-153). 
III. PERIPHERAL NERVOUS SYSTEM. 
(There are some advantages in dissecting the eye with its muscles 
before dissecting the nerves, as a knowledge of the eye-muscles is 
presupposed for dissecting some of the cranial nerves. For directions 
on the eye, see p. 469.) 
A new specimen should be used, if possible, for the peripheral 
nervous system, though that used for the blood-vessels can be 
employed, at considerable disadvantage. ‘ 
Prepare as for the blood-vessels. The arteries should be injected 
with red starch, to aid in tracing the nerves. 
1. Tue Craniat Nerves (p. 369) AND SYMPATHETIC SYSTEM (p. 404). 
1. Reflect the skin covering the sternomastoid muscle, and make 
a longitudinal incision of the muscle so as to expose the carotid 
