THE MAMMALIAN NERVOUS SYSTEM 93 



(see Section 96) . At the lower end of the oblongata caudad of 

 the inferior olive this tract, together with the spinal lemniscus, 

 can be recognized, in the gross preparation, lying immediately 

 ventrally of the tr. spino-cerebellaris dorsalis of Flechsig and 

 dorsally and laterally of the olive. Dissect the mixed bundle 

 out in this position and trace it forward. It can be followed to 

 a level near the pons. Its further course (which cannot easily 

 be dissected) is as follows (see Section 107) : At about the level 

 of the upper border of the pons the fibers of the ventral spino- 

 cerebellar tract separate from the lemniscus fibers and turn 

 abruptly dorsalward, then backward, to enter the brachium 

 conjunctivum. Through the brachium conjunctivum they 

 enter the vermis of the cerebellum medially of the dentate 

 nucleus. 



106. The cochlear nuclei and lateral lemniscus. — Determine 

 again the positions of the cochlear and vestibular roots of the 

 VIII nerve. Identify the dorsal and ventral cochlear nuclei. 

 Fibers from the dorsal nucleus (striae medullares acusticse) 

 can be followed across the floor of the fourth ventricle. At 

 the midline these fibers decussate and pass ventralward to the 

 superior olive of the opposite side. From the ventral cochlear 

 nucleus fibers of the trapezoid body pass ventralward and medial- 

 ward, at first embedded in the deepest fibers of the pons. They 

 reach the superior olive of the same and the opposite side. 

 They can be dissected, though their separation from the deep 

 fibers of the pons is very difficult. From the superior olive 

 of the opposite side the conduction path which continues both 

 the dorsal and the ventral cochlear pathways (stria? medullares 

 and trapezoid bodies respectively) is the lateral lemniscus, whose 

 fibers terminate in the colliculus 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. These fibers lie dorsally of those of the cere- 

 bral peduncle and superficially of those of the brachium con- 



