374 



THE NERVOUS SYSTEM 



By this dissection the insula and the dorsal surface of the temporal lobe have been ex- 

 posed. Note in particular the transverse temporal gyri. 



125. Now dissect away the dorsal part of the temporal lobe and remove the insula. 

 This will expose the uncinate and inferior occipitofrontal fasciculi as well as the external 

 capsule (Fig. 227). These fiber bundles can best be displayed by carrying the dis- 

 secting instrument in the direction of the fibers. Complete the dissection of the corona 

 radiata and the optic radiation (Fig. 227). 



126. Now turn the specimen over and make a dissection of the column ofthefornix 

 and the mamillothalamic tract as in Fig. 205, but do not cut away the brain stem as 

 indicated in that figure. 



127. Dissection of the Internal Capsule from the Medial Side (Fig. 195). Tear 

 away the fornix and septum pellucidum, opening up the lateral ventricle. With the 

 brain knife cut away a slice from the medial surface of the hemisphere, varying in thick- 

 ness from T inch at the frontal end to i inch at the occipital end, cutting through the 

 corpus callosum and into the ventricle, but not into the basal ganglia. With a scalpel 

 and tissue forceps remove what remains of the medial wall of the lateral ventricle, 

 except in the inferior horn. Grasp with tissue forceps the stria terminalis in the rostral 

 end of the sulcus terminalis and tear it away, carrying the forceps toward the occipital 

 pole (p. 214). By blunt dissection remove the thalamus and subthalamus as well as the 

 tegmentum and corpora quadrigemina of the mesencephalon. In scraping away these 

 parts carry the dissecting instrument from the sulcus terminalis in a ventral direction. 

 This will uncover the basis pedunculi and its continuation into the internal capsule. 

 The fibers of the thalamic radiation will be broken off at the point where they enter the 

 internal capsule (Fig. 195). Remove the ependymal lining of the posterior horn of the 

 ventricle and uncover the tapetum. Scrape away the caudate nucleus, carrying the 

 dissecting instrument in the direction of the fibers of the internal capsule (Fig. 195). 

 Trace the anterior commissure to the point where it disappears under the anterior 

 limb of the internal capsule. Study the internal capsule as seen from the medial sur- 

 face, and note particularly the direction of the fibers, the anterior limb, the posterior 

 limb, the optic radiation, and the curved ridge which represents the genu, 



128. Now turn again to the lateral side of the specimen (Fig. 227), and grasping 

 with tissue forceps individual strands of the uncinate fasciculus in temporal lobe strip 

 them forward into the frontal lobe. Remove the entire fasciculus in this manner. In 

 the same way strip away the fibers of the inferior occipitofrontal fasciculus, beginning 

 in the frontal lobe and tracing them toward the occiput. Strip off the fibers of the ex- 

 ternal capsule and expose the lentiform nucleus and the corona radiata (Fig. 194). 

 Pay special attention to the fibers of the corona radiata which come from the sublen- 

 ticular part of the internal capsule and enter the temporal lobe. Follow the anterior 

 commissure to the point where it disappears under the lentiform nucleus. 



129. Remove what remains of the temporal lobe and examine the hippocampus, 

 fimbria, and inferior horn of the lateral ventricle from the dorsal surface (Fig. 201). 



130. Next scrape away the lentiform nucleus and trace the basis pedunculi into the 

 internal capsule (Fig. 88). Study the corona radiata, internal capsule, and basis 

 pedunculi from both sides of this preparation. The thalamus and the caudate and 

 lentiform nuclei produce well-marked impressions on the internal capsule (Figs. 88, 195). 



