98 LABORATORY OUTLINE OP NEUROLOGY 



Identify the medial lemniscus in the region of the superior 

 olive. It will be found as a broad band of longitudinally 

 directed fibers near the midplane immediately dorsally of the 

 deepest fibers of the pons. Tracing them downward they be- 

 come crowded into the space between the two inferior olives. 

 Under the nuclei of the fasciculus gracilis and fasciculus cune- 

 atus these fibers cross the midplane and then turn abruptly 

 dorsalward in numerous strands to connect with these nuclei 

 of the opposite side. 



In the dissection of the medial lemniscus in the medulla ob- 

 longata care must be taken not to destroy the pyramidal tract 

 which lies ventrally of it and the fasciculus longitudinalis 

 medialis and tecto-spinal tract which lie dorsally of it. 



In the midbrain the medial lemniscus fibers split off from 

 those of the lateral lemniscus shortly before the latter enter 

 the inferior colliculus and the medial geniculate body (Herrick 

 ('18), Fig. 75). The medial lemniscus continues almost di- 

 rectly forward, lying ventrally and medially of the lateral 

 lemniscus, and ends in the lateral and ventral nuclei of the 

 thalamus (Herrick ('18), Figs. 77 and 78), but at this stage of 

 the work it should not be dissected farther forward than the 

 midbrain. 



109. The fasciculus longitudinalis medialis. In the me- 

 dulla oblongata the fibers of the fasciculus longitudinalis 

 medialis (posterior longitudinal bundle) will be found running 

 close to the median plane and immediately under the floor of 

 the ventricle. In the lower parts of the medulla this tract lies 

 dorsally of the medial lemniscus and separated from it only by 

 the tecto-spinal tract, but in the pons region and midbrain 

 these two tracts are far separated. In the dissection of this 

 tract work from the cut median surface lateralward and do not 

 disturb the floor of the fourth ventricle (cf. Sections 92 and 93). 



110. The fasciculus solitarius. The fasciculus solitarius can 

 now be dissected out. Locate again the ala cinera (trigonum 

 vagi) in the floor of the fourth ventricle. This marks the posi- 

 tion of the dorsal vagal nuclei. Tease off these superficial gray 

 masses and expose the slender fasciculus solitarius which lies 

 below them. Follow this tract downward and upward to its 

 ends (cf. Section 84). 



