38 Anatomy of the Nervous System 



the trapezoid body by thick bundles of trapezoid fibres. Its connections 

 are similar to those of the other part of the nucleus. 



The nucleus of the trapezoid body lies medio-ventral to the last- 

 mentioned group and is differentiated from the more ventro-laterally 

 placed nucleus praeolivaris internus by its larger cells. It is traversed by 

 many longitudinal fibre bundles. There are extensive fibre connections 

 with the lateral parts of the medial lemniscus and the pyramidal tract as 

 well as with the accessory superior olivary nucleus, but none with the 

 lateral lemniscus of the same side. There are considerable heterolateral 

 connections also. 



The nucleus praeolivaris internus receives fibres of the corpus trape- 

 zoides, mostly of heterolateral origin. The lateral part of the nucleus 

 sends most of its axons across the raphe, while most of those from the 

 medial part enter the homolateral medial lemniscus and pyramidal tract. 



The dorsal accessory nucleus of the principal superior olive lies over 

 the dorsal hilus of the latter in relation to the fibres of v. Monakow. 



The trapezoid fibres ending in the principal superior olivary nucleus 

 are partly hetero- but chiefly homolateral in origin and only about one- 

 quarter to one-third of the fibres coming directly from the cochlear nuclei 

 decussate. These apparently originate chiefly in the ventral cochlear 

 nucleus. The crossed fibres of the trapezoid body originating in the nucleus 

 of the trapezoid body, superior accessory olivary nucleus, nucleus prae- 

 olivaris internus, ventral cochlear nucleus, dorsal cochlear nucleus and 

 chief superior olivary nucleus are of decreasing numerical importance in 

 the order named, and are accompanied by a few fibres from the spinal 

 V nucleus and from the reticular formation. Most of these fibres are 

 distributed more caudally after decussating, while most of those from 

 the cochlear nucleus end in the olivary complex. Apart from the fibres 

 of V. Monakow, the lateral lemniscus is very largely of homolateral origin. 



The lateral lemniscus passes directly forwards into the 

 midbrain, where many of its fibres may be followed into the 

 posterior colliculus (p. 68). Others pass on with the fibres 

 arising in that region to the medial geniculate body (p. 79). 

 In the lower part of its course, the fibres of the lateral lem- 

 niscus enclose a group of cells, the ventral nucleus of the lateral 

 lemniscus {nucleus ventralis Umnisci lateralis), in connection 

 with which a number of them end. The lemniscus then 

 follows a somewhat antero-dorsal course and breaks up into 

 small fibre-bundles as it approaches the midbrain. Between 



