1258 



HUMAN ANATOMY. 



origin (Fig. 1071). Not all of the fibres arising from the superior ohvary nucleus, however, 

 enter the lateral fillet. A considerable number leave the dorsal surface of the nucleus and, as 

 its peduncle, pass to the abducent nucleus and, by way of the posterior longitudinal fasciculus, 

 to the nuclei of the other eye-muscle nerves. In this manner refle.x paths are established by 

 which the motor nerves, including probably the facial, are brought under the influence of audi- 

 tory impulses. Within the tract of the fillet and a short distance beyond the superior olive, is 

 encountered a group of nerve-cells, the nucleus of the lateral fillet (nucleus lemnisci lateralis). 

 While numerous additions to the fillet are received from these cells, their relation to the cochlear 

 fibres is uncertain. The characteristics, course and destination of the lateral fillet have been 

 elsewhere described (page 1082). Suffice it here to recall that, so far as the auditory fibres are 

 concerned, the tract terminates chiefly in the inferior coUiculus of the quadrigemina and the 

 median geniculate body. 



In addition to its constituents through the corpus trapezoides, the lateral fillet receives con- 

 siderable accessions of cochlear fibres by way of the striae acusticae. These strands consist of 

 the axones, for the most part, of the cells lying within the tuberculum acusticum, but to a limited 



Fig. 107 1. 



Diagram showing connections of auditory nerve ; cochlear fibres and connections are in black, vestibular in red; 

 C, cochlea; GS, ganglion spirale; lAC, internal auditory canal ; VC, DC, ventral and dorsal cochlear nuclei ; RB, 

 restiforni body ; SO, superior olive ; 77?. trapezoid body ; Ac St, acoustic striae ; Nlf, nucleus of lateral fillet [LF) ; 

 MF, median fillet; /g, inferior quadrigeminal body; MG, median geniculate body : ^^, auditory radiation ; TC, 

 temporal cortex; T, thalamus; SC, semicircular canal; K, vestibule ; VG, vestibular ganglion; AfK, median 

 vestibular nucleus ; DN, lateral (Deiters') vestibular nucleus; Vsp, vestibulo-spinal fibre; Ci, cerebellum. 



extent also of the axones of the ventral cochlear nucleus, which wind over the latero-dorsal 

 surface of the inferior cerebellar peduncle, pass medially beneath the ependyma of the floor of 

 the fourth ventricle as far as the median groove, and, crossing to the opposite side, then sweep 

 ventrally through the dorsal region of the medulla or pons to join the tract of the lateral fillet, 

 and so proceed in company with the other cochlear fibres to the higher levels. By no means 

 all of the component fibres of the acoustic striae follow the lateral fillet, since some after decussa- 

 tion turn brainward, possibly joining the mesial fillet, whilst others may enter the posterior 

 longitudinal fasciculus to assist in establishing reflex paths influencing the motor nerves. 



The auditory path, by which the impulses gathered from the organ of Corti by the cochlear 

 fibres are conducted to the cerebral cortex, includes the following components (Fig. 1071 ) : 



1. Peripheral neurones of the ganglion spirale, whose axones (the cochlear fibres) pass to 

 the reception-nucleus (ventral and lateral cochlear nuclei). 



2. Neurones of the cochlear nuclei, which send their axones : {a) by way of the corpus 

 trapezoides to the superior olivary nucleus, chiefly to that of the opposite side but also to that 

 of the same side, or to the lateral fillet or its nucleus without interruption in the olive ; {b) by 

 way of the striae acusticae through the tegmentum to join the trapezoidal fibres. 



3. Neurones of the superior olivary nucleus or of the fillet-nucleus, whose axones pass by 

 way of the lateral fillet [a) to the cells within the inferior coUiculus, or {b) without interruption 

 through the inferior brachium to the cells within the median geniculate body. 



