A LABORATORY OUTLINE OF NEURO-ANATOMY 373 



118. In the frontal sections of the left cerebral hemisphere of the human brain study 

 the relations of the septum pellucidum, fornix, fimbria, hippocampus, and anterior 

 commissure (Figs. 186-190). 



119. The Cerebral Cortex. On the right hemisphere of the human brain identify 

 the motor, somesthetic, auditory, and visual centers (Figs. 220, 221; pp. 290-293). 

 With a scalpel remove a cube of cortex and subjacent white matter from each of these 

 areas. Each block should measure about 1 cm. in each dimension. With a sharp 

 razor make section through each of these blocks at right angles to the surface of the cortex 

 and perpendicular to the long axis of the gyrus from which the block was cut. Note the 

 differences in thickness of the cortex in the various regions. Observe the white 

 striations in the cortex, and note how these differ in the several specimens (Fig. 218). 

 Study the stained and mounted sections of the cerebral cortex which are furnished 

 you. What details of cell and fiber lamination do these preparations show, and how 

 does this lamination differ in the several regions of the cortex? (See Fig. 215; pp. 

 284-287.) 



120. Association Fibers (Figs. 226, 228; pp. 298-301). If the human brain is reason- 

 ably well preserved the larger bundles of association fibers may be easily exposed by 

 dissection. This can be done on the right hemisphere. But if the material is very 

 soft this half of the brain can more profitably be laid into a series of horizontal sections 

 and these used for a review of the form and relations of the component parts of the 

 cerebral hemisphere. If the material is fairly well preserved, make the following 

 review dissection and at the same time expose and study the various bundles of asso- 

 ciation fibers. 



121. Review Dissection of the Human Brain. Take the right half of the 

 human brain and scrape away the cerebral cortex from a portion of the dorsal 

 surface of the frontal lobe. This will expose the short association or arcuate fibers 

 (Fig. 226). 



122. Now make a horizontal section through the hemisphere parallel to the dorsal 

 surface of the corpus callosum and J- inch dorsal to it. Note the centrum semiovale. 

 Scrape away the cortex of the gyrus cinguli and the white matter immediately sub- 

 jacent to it. In making this dissection carry the orangewood stick in an anteroposterior 

 direction, removing the white matter a little at a time until a longitudinal bundle of 

 fibers, the cingulum, is exposed (Fig. 174). The indusium griseum and striae longi- 

 tudinales should now be uncovered. 



123. Remove the cingulum, scrape away the indusium griseum, and expose the 

 radiation of the corpus callosum as indicated on the right side of Fig. 174, but do not 

 cut the optic radiation or expose the tapetum at this time. 



124. Remove the parietal operculum a little at a time. This can be done with 

 tissue forceps. Grasp small portions and t^ar them away by upward traction. Note 

 the bundles of transverse fibers which enter this operculum from the corpus callosum 

 and internal capsule. These intersect at right angles with the fibers of the superior 

 longitudinal fasciculus which should come into view as the dissection progresses (Fig. 

 174). The transverse bundles should be made to break off at the point where they pass 

 through the superior longitudinal fasciculus. Complete the dissection of this fasciculus, 

 carrying the dissecting instrument in the direction of its fibers. Now demonstrate the 

 intersection of the corona radiata w r ith the radiation of the corpus callosum (Fig. 174). 



