112 LABORATORY OUTLINE OF NEUROLOGY 



ham ('15), pp. 814-818; Herrick ('18), Figs. 97-99; Howell 

 ('18), Chap. XVIII. On the general structure of the eye, see 

 Section 14. 



136. Optic system. In the sheep dissection remove the hip- 

 pocampus. Identify the structures on the lateral surface of 

 the thalamus and midbrain: pulvinar, lateral and medial 

 geniculate bodies, superior and inferior colliculi. Follow the 

 optic. tract from the chiasma to the thalamic optic centers 

 (pulvinar and lateral geniculate body), where the thalamic 

 optic fibers terminate. Trace other fibers of the optic tract 

 over the surface of the medial geniculate body to the superior 

 colliculus of the midbrain (optic tectum). This is the center 

 for the optic reflexes of accommodation, etc. 



By teasing away the gray matter of the pulvinar, optic pro- 

 jection fibers can be followed from the pulvinar to the occipital 

 pole of the cerebral hemisphere. The pulvinar and lateral 

 geniculate body are the thalamic centers, which, through their 

 connections with the cerebral cortex, provide for conscious 

 visual responses. See Bailey ('16), Fig. 358, p. 534; Cunning- 

 ham ('15), pp. 619, 620; Edinger ('11), Fig. 220, p. 296; Gray 

 ('18), Figs. 773, 774, pp. 882, 883; Herrick ('18), Chap. XIV; 

 Morris ('14), Figs. 655-660, pp. 844, 845, Fig. 670, p. 849; 

 Piersol ('16), pp. 1223-1225; Quain ('09), Vol. Ill, Pt. I, Figs. 

 232, 233, pp. 228, 229, Fig. 243, p. 240; Rauber-Kopsch ('12), 

 Figs. 109, 111, 112, 123, 124, 261; Villiger ('12), pp. 172-174. 



137. Auditory system. The medial geniculate body of the 

 sheep (thalamic auditory center) and the inferior colliculus 

 (midbrain auditory center) should again be located (Fig. 12), 

 also the arm of the inferior colliculus (brachium quadrigem- 

 inum inf erius) , which is the auditory path between the inferior 

 colliculus and the medial geniculate body. 



Auditory projection fibers pass from the medial geniculate 

 body through the internal capsule to the temporal lobe of the 

 cerebral cortex, but these cannot well be separated by dissec- 

 tion in the sheep. 



138. Dissection of the pyramidal tract. As the last step of 

 the sheep dissection, by careful tearing down of the fibers follow 

 out some of the internal capsule fibers into the regions of the 

 thalamus, midbrain, and medulla oblongata. Try especially 



