PRACTICAL DIRECTIONS. 465 



foramen ot Monro, 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)- 



/. Remove the choroid plexus or roof of the third ventricle and 

 study again the thalami (Fig. 141). 



g. IMake 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). 



h. 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. 



I. The Cranial Nerves (p. 369) and Sympathetic System (p. 404). 



I. Reflect the skin covering the sternomastoid muscle, and make 

 a longitudinal incision of the muscle so as to expose the carotid 

 artery. Lying along the artery find the combined trunk of the 



