A LABORATORY OUTLINE OF NEURO-ANATOMY 369 



Follow the aqueduct into the third ventricle, removing from the latter the remains of 

 its left lateral wall. Care is required in removing the rostral part of this wall in order 

 that the lamina terminalis may be left intact. Now remove such portions of the left 

 cerebral cortex as are still attached to the preparation. By this dissection a much more 

 instructive preparation is obtained than when the original section is made exactly in 

 the median plane. 



92. Take the left lateral hah of the sheep's brain and tear away what remains of the 

 septum pellucidum and body of the fornix and locate the caudate nucleus. For the 

 identification of these structures see Figs. 84 and 204. ^ Cut through the internal capsule, 

 which has previously been exposed from the lateral side in this specimen, along a line 

 extending horizontally toward the occipital pole from the highest part of the dorsal 

 border of the caudate nucleus. Remove the portion of the cerebral hemisphere that 

 lies dorsal to the plane of this section and thus expose the dorsal surface of the thalamus 

 (Fig. 91). 



93. Diencephalon. Study the thalamus as it appears in all of these preparations 

 (pp. 213-216). Examine the dorsal surface of the thalamus on the left half of the sheep's 

 brain (Figs. 89, 91, 180). The lateral surface of the thalamus rests against the internal 

 capsule, as can be readily understood from a study of this dissection. The medial 

 surface forms a part of the wall of the third ventricle (Figs. 158, 159). 



94. Study the epithalamus in both the human and the sheep's brain. Of what 

 parts is it composed? (See Figs. 91, 158, 159; pp. 220, 221.) 



95. Locate all the parts which belong to the hypothalamus in both the human and 

 the sheep's brain (Figs. 84, 86, 158, 159; pp. 222, 223). 



96. Study the shape and boundaries of the third -ventricle (Figs. 158, 159; pp. 

 223, 224). 



97. The Metathalamus. On the left half of the sheep's brain identify the medial 

 geniculate body (Fig. 87). Immediately rostral to this body is a slight elevation in the 

 optic tract produced by the subjacent lateral geniculate body. Identify both of these 

 bodies on the human brain (Figs. 88, 89, 154). 



98. In the frontal sections of the left human cerebral hemisphere identify the various 

 parts of the diencephalon (Figs. 188, 189). From these sections something can be 

 learned concerning the internal structure of the thalamus, but more information can 

 be obtained on this subject from sections stained by the Weigert method (Figs. 156, 

 157; p. 216). In these sections trace the basis pedunculi into the internal capsule and 

 the medial lemniscus into the thalamus. 



99. Dissection of the Optic Tract Take the left lateral half of the sheep's brain 

 and, grasping the optic chiasma with the tissue forceps, pull the optic tract lateralward, 

 separating it from the surface of the peduncle. It separates easily until the position 

 of the lateral geniculate body is reached just rostral to the medial geniculate body. 

 Stronger traction will cause it to tear away from the lateral geniculate body, which is 

 now exposed as a prominent curved ridge of gray matter. This nucleus extends rostrally 

 and dorsally from the medial geniculate body and is continuous with the pulvinar of 

 the thalamus. Continued traction will cause the optic fibers to strip off from the sur- 

 face of the pulvinar. Here they form a rather thick white lamina, the stratum zonale. 

 Continue the dissection, raising the fibers of the optic tract as far as the groove rostral to 

 the superior colliculus. Now cut the transverse peduncular tract, which lies in this 



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