COMPOSITION AND CENTRAL CONNECTIONS OF CRANIAL NERVES 859 



I The lateral preolivary or semilunar nucleus lies ventral to the superior olivary 

 nucleus. In it end terminals and collaterals of the trapezoid body and probably 

 fibers of the opposite cochlear nucleus. Its axons mingle with the trapezoid body 

 and join the lateral fillet. 



The mesial preolivary nucleus is in contact with the ventral side of the nucleus 

 of the trapezoid body. It receives many collaterals from the trapezoid body. Its 

 cells are smaller than those of the trapezoid nucleus, their axons join the lateral 

 fillet. 



The lateral lemniscus (lateral fillet} , the continuation upward of the central path 

 of hearing, consists of fibers which come from the cochlear nuclei of the same and 

 the opposite side by way of the trapezoid body and from the preolivary nuclei. It 

 lies in the ventral or ventro-lateral part of the reticular formation of the pons, at 



) first ventral then lateral to the median fillet. Above the pons these ascending fibers 

 come to the surface at the side of the reticular formation in the trigonum lemnisci 

 and are covered by a layer of ependyma. This part of the lateral lemniscus is 

 known as the fillet of Reil. On reaching the level of the inferior colliculus the dorsal 

 fibers which overlie the superior peduncle decussate in the velum medullare anterius 

 with similar fibers of the opposite side. Numerous small masses of cells are scattered 

 along the path of the lateral lemniscus above the superior olivary nucleus and con- 

 stitute lower and upper nuclei of the lateral lemniscus. They are supplied with 

 many collaterals and possibly terminals from the fibers of the lemniscus. The axons 

 of the lower nucleus of the lateral lemniscus, which arise from the larger stellate or 

 spindle-shaped cells, with long, smooth, much branched dendrites, are said by some 

 authors to join the lateral lemniscus, but according to Cajal they pass medially 

 toward the raphe; their termination is unknown. The cells of the upper nucleus 

 of the lateral lemniscus are more scattered. The same uncertainty exists in regard 

 to their termination. 



The fibers of the lateral lemniscus end by terminals or collaterals in the inferior 

 colliculus and the medial geniculate body. A few of the fibers are said to pass by 

 the inferior colliculus to terminate in the middle portion of the stratum griseum of 

 the superior colliculus, and are probably concerned with reflex movements of the 

 eyes depending on acoustic stimuli. 



The inferior colliculi (lower or posterior qitadrigeminal bodies} are important 

 auditory reflex centers. Each consists of a compact nucleus of gray matter covered 

 by a superficial white layer and separated from the central gray matter about 

 the aqueduct by a thin, deep, white layer. Many of the axons which appear in the 

 superficial white layer ascend through the inferior brachium to the medial genicu- 

 late body. Others mainly from large cells in the dorso-mesial part of the nucleus 

 pass through the deep white layer into the tegmentum of the same and the opposite 

 side and descend. Their termination is unknown, but they probably constitute an 

 auditory reflex path to the lower motor centers, perhaps descending into the spinal 

 cord with the tectospinal fasciculus. Other axons are said to descend in the lateral 

 lemniscus to the various nuclei in the auditory path (Held) and probably to motor 

 nuclei of the medulla and spinal cord. 



The medial geniculate body receives terminals and collaterals from the lateral 

 lemniscus (the central auditory path) and also large numbers of axons from the 

 inferior colliculus of the same side and a few from the opposite side. It is thus a 

 station in the central auditory path. A large proportion of its axons pass forward 

 beneath the optic tract to join the corona radiata and then sweep backward and 

 lateralward as the auditory radiation to terminate in the cortex of the superior 

 temporal gyrus. V. Monakow holds that Golgi cells type II are interpolated between 

 the terminations of the incoming fibers to the medial geniculate body and the cells 

 located there which give rise to the fibers of the auditory radiation. The medial 

 geniculate bodies are united by the long, slender commissure of Gudden. These 





