THE NERVOUS SYSTEM 



groove, by making a superficial incision across the groove along the lateral border of 

 the optic fibers. Scrape away the superficial gray matter (about 1 mm.) of the superior 

 colliculus and expose the stratum opticum (Fig. 116). Now continue the traction on 

 the optic tract and a striking demonstration will be obtained of the fact that the stratum 

 opticum is composed of fibers from this tract (Figs. 161, 162; pp. 226, 227). 



100. Dissection of the Optic Radiation. In the left half of the sheep's brain scrape 

 away part of the gray matter of the pulvinar. Follow fibers from the pulvinar into the 

 posterior limb of the internal capsule. These belong to the optic radiation, which may 

 now be followed by dissection to the cortex near the occipital pole of the cerebral hemi- 

 sphere (Fig. 260; pp. 227, 228). Now take the right half of the cerebral hemisphere 

 and identify the visual area of the cerebral cortex (Fig. 221). 



Optic radiation ' ' /* 

 Superior colliculus:' / 

 Inferior colliculus ' \ 



Pulvinar '^| 

 Medial geniculate body '" 

 Cerebral peduncle 



Mammillary body 



Optic tract 

 Posterior limb of internal capsule 



Optic nerve 



Intersection of corona radiata and 



radiation of corpus callosum 

 Anterior limb of internal capsule 

 Anterior perforated substance 



Fig. 260. Dissection of the cerebrum of a sheep showing the internal capsule and corona radiata. 

 The lentiform nucleus has been removed. 



101. Surface Form of the Cerebral Hemispheres. Compare the basal surface of the 

 human brain with that of the sheep. Note in each the parts belonging to the rhinen- 

 cephalon and locate the rhinal fissure, which separates the neopallium and the archi- 

 pallium. Nearly all of the surface of the human cerebral hemisphere is formed by the 

 neopallium (Figs. 83, 86; pp. 115, 116). 



102. Examine the right cerebral hemisphere of the human brain and identify the 

 poles, fissures, sulci, lobes, and gyri (Figs. 166-168, 170, 171; pp. 232-242). Draw 

 the margins of the lateral fissure apart and locate the insula (Fig. 169). Study 

 the insula in the frontal sections through the left cerebral hemisphere (Figs. 186-189; 

 p. 237). 



103. Internal Configuration of the Cerebral Hemisphere. Take the sheep's brain 

 from which the cerebellum has been removed and slice away successive thin layers from 

 the dorsal aspect of both hemispheres. These thin sections should be cut in planes 

 parallel to the dorsal surface of the corpus callosum and the last cut should be inch 

 dorsal to that commissure. The direction and relative depth of the dorsal surface of 



