THE MAMMALIAN NEKVOUS SYSTEM 97 



inferior of the midbrain and the medial geniculate body of the 

 thalamus. This portion of the lateral lemniscus can best be 

 dissected from above downward (cf. Sections 81 and 82). 



Lift up the occipital pole of the cerebral hemisphere and 

 locate the superior and inferior colliculi on the dorsal surface of 

 the midbrain. Extending backward and downward from the 

 inferior colliculus is a flat ridge formed by the fibers of the 

 lateral lemniscus (Herrick ('18), Fig. 45; Cunningham ('15), 

 Fig. 517). These fibers lie dorsally of those of the cerebral 

 peduncle and superficially of those of the brachium con- 

 junctivum; at the upper border of the pons they turn inward 

 and can be followed downward dorsally of the deep fibers of the 

 pons to the superior olive. This small nucleus is difficult 

 to identify, since its cell bodies are scattered among the fibers, 

 but its position is indicated at the place where the lemniscus 

 fibers turn abruptly medialward. (Compare the next para- 

 graph for the relations of the spinal lemniscus to the lateral 

 lemniscus and Section 82 for the microscopic appearance of this 

 region.) 



107. Having traced the fibers of the lateral lemniscus back- 

 ward to the superior olive, the ventral spino-cerebellar tract 

 (of Gowers) and the spinal lemniscus (see Section 105) may now 

 be traced from the lower border of the pons to the upper bor- 

 der of the superior olive, where they will be seen to accompany 

 the lateral lemniscus from this level forward. The ventral 

 spinocerebellar tract accompanies the lateral lemniscus com- 

 plex into the midbrain, where its fibers may be seen to sepa- 

 rate from the others and to enter the cerebellum by the way 

 of the brachium conjunctivum, lying more superficially than 

 the tract, from the dentate nucleus to the red nucleus. 



108. The medial lemniscus. Identify again the nucleus 

 of the fasciculus gracilis and the nucleus of the fasciculus 

 cuneatus. These receive proprioceptive fibers from the spinal 

 cord by way of the fasciculus gracilis and fasciculus cuneatus. 

 The cell bodies of these nuclei send their axones to the thala- 

 mus by way of the medial lemniscus. In the pons region this 

 lemniscus lies ventrally and medially of the superior olive and 

 medially of the lateral lemniscus, whose fibers it adjoins during 

 their course through the upper pons and midbrain regions. 



