372 THE NERVOUS SYSTEM 



brain note that the tail of the caudate nucleus extends ventrally into the roof of the 

 inferior horn of the lateral ventricle. With a blunt instrument scrape away the head 

 and first part of the tail of the nucleus, exposing the medial surface of the internal cap- 

 sule (Fig. 91). Note the shape and size of this nucleus as you are removing it. 



110. Study a horizontal section stained by the Weigert method through the internal 

 capsule and basal ganglia. From this section and from the dissections endeavor to 

 form a clear mental picture of the internal capsule and its relations (Figs. 191, 193; 

 pp. 257-261). 



111. Now take the frontal sections of the left hemisphere of the human brain 

 and identify the various parts of the corpus striatum and internal capsule (Figs. 186- 

 190). 



112. Rhinencephalon. Study the olfactory portions of the brain to be seen on the 

 ventral surface of the cerebral hemisphere in the human and sheep's brains (Figs. 172, 

 197, 199 ; pp. 265-269) . Study the hippocampus, alveus, and fimbria as they lie exposed 

 in the inferior horn of the lateral ventricle of the sheep's brain (Figs. 178, 182). Open 

 up the inferior horn of the lateral ventricle on the left side of this specimen so as to 

 expose the hippocampus and fimbria. Raise the hippocampus and fimbria on both sides 

 at the same time, leaving them still attached to the fornix. This should be done without 

 damaging the underlying tela chorioidea of the third ventricle, which occupies the great 

 transverse fissure. Examine the under surface of the hippocampus, fimbria, and for- 

 nix. Note that the two fimbriae unite to form the triangular body of the fornix. 

 The transverse fibers in this triangle constitute the hippocampal commissure (lyra). 

 Note the fascia dentata and hippocampal fissure. Figure 204 will help you to interpret 

 the parts seen in this dissection. 



113. The chorioid plexuses of the prosencephalon are now fully exposed, and their 

 relations to each other and the brain ventricles can be readily studied (pp. 224, 251). 



114. Remove the tela chorioidea of the third ventricle and again identify the parts 

 of the thalamus and epithalamus which may be seen from above (Figs. 91, 180). 



115. Replace the fornix and hippocampus in position and divide the fornix and what 

 remains of the cerebral hemispheres by a sagittal section \ millimeter to the right of 

 the median plane. Take the left half of the preparation and, tearing away any por- 

 tions of the right columna fornicis that may still be attached to the preparation, follow 

 the left column of the fornix to the mammillary body. This can be accomplished by 

 scraping away some of the medial surface of the thalamus (Fig. 204). At the same time 

 expose the mamillothalamic tract. Remove the posterior part of the thalamus and the 

 remainder of the brain stem by a cut made just caudal to the mamillothalamic tract, 

 as indicated in Fig. 204. This gives a connected view of the entire fornix system. 

 Find the cut surface of the hippocampal commissure and separate it for a few milli- 

 meters from the rest of the fornix. Identify again the fimbria, fascia dentata, hippo- 

 campal fissure and hippocampal gyrus, and study the fornix as a whole (Figs. 200, 

 203; pp. 270-272). 



116. Study the septum pellucidum in the right half of the human brain (Fig. 158; 

 p. 272). Also locate the anterior commissure. 



117. Dissect the anterior commissure in the right lateral half of the sheep's brain. 

 Locate the commissure on the median surface and by blunt dissection follow it to the 

 olfactory bulb (Fig. 199; p. 273). 



