THE MAMMALIAN NERVOUS SYSTEM 71 



ficial fibers compose the lateral lemniscus. They occupy a 

 triangular area bounded by the pons behind, the basis pedunculi 

 (pyramidal and cortico-pontile tracts) below, and the corpora 

 quadrigemina above. 



Beginning at the cut medial surface, strip back the fibers of 

 the pons as far laterally as the roots of the V nerve. Immedi- 

 ately ventrally of these root-fibers careful teasing with a sharp- 

 ened wooden instrument will show that some fibers of the 

 trapezoid body turn from the transverse to the longitudinal 

 direction and, passing internal to the pons fibers; reappear on 

 the surface in front of the pons as the lateral lemniscus fibers, 

 to which reference has already been made. At the point where 

 they turn and are covered by the overlying pons fibers a small 

 nucleus of gray matter may be found. This is the superior 

 olive. By gentle teasing the lateral lemniscus fibers may be 

 followed from the level of the pons forward and dorsal ward. 

 Some enter the medial geniculate body of the thalamus and 

 some enter the inferior colliculus. The latter are interrupted 

 by a synapse here and the acoustic path is then continued for- 

 ward through the brachium of the inferior colliculus to enter the 

 medial geniculate body in company with the component first 

 described. 



The secondary acoustic path is thus seen to ascend from the 

 cochlear nuclei of one side by way of the lateral lemniscus to the 

 medial geniculate body of the thalamus of the opposite side. 

 Some of these fibers enter the thalamus directly and some are 

 first interrupted by a synapse in the inferior colliculus. 



For the dissection of the lateral lemniscus in the human 

 brain, see Section 106. 



82. Microscopic study of the cochlear nuclei and lateral lem- 

 niscus. — Now in the microscopic sections of the human brain 

 stem locate the structures described in the last section (see 

 Section 62 (5)). 



Identify the dorsal and ventral cochlear nuclei and the striae 

 medullares acusticse. The fibers of the trapezoid body may not 

 be easily distinguished from the deepest fibers of the pons which 

 he ventrally of them. The superior olive is a small gray nucleus 

 lying deeper than any of these fibers and laterally of the great 

 medial lemniscus tract (medial fillet) . If the lateral lemniscus 



