496 THE BRAIN OF MAMMALS, BY TH. MEYNEET. 



anterior nucleus of the facial (fig. 255) ; the superior conducts 

 them from the genu outwards and forwards to the point of 

 emergence (fig. 254, on the right side). The genu forms a 

 connecting piece at right angles to the two crura. The horse- 

 shoe, however, in order to curve round the common nucleus 

 (as far as its median surface), bends inwards at the intermediate 

 piece (as if along the surface), and at the same time, in order 

 to curve round the upper circumference of this nucleus, bends 

 upwards to the upper crus (as though along the edge). 



The uppermost arched fibres of the root of the facial, proceeding 

 from the genu, extend upwards as far as to the origin of the fifth 

 (fig. 253, 7) ; and hence the statement made by Stilling, that the genu 

 of the facial was a constant posterior root of the fifth, and that its 

 terminus was an inferior trigeminal instead of a facial nucleus. 



The roots of the auditory nerve are met with at about the 

 same plane as the origin of the ascending root of the facial 

 (fig. 255, 8), and the following four formations of grey matter 

 stand in connection with them in the pons : 



1. The internal auditory nucleus (Stilling, Clarke). In this 

 an upper, middle, and inferior plane are to be distinguished. 

 The upper is situated externally to the arch of the superior 

 nucleus of the facial (fig. 254, 8) ; the middle (corresponding 

 nearly to the zone of the striae medullares) includes the entire 

 breadth of the rhomboidal space (fig. 255, vin) ; and the in- 

 ferior lies externally to the origin of the glossopharyngeus and 

 to the nucleus of the vagus and accessory nerves (fig. 257, 8). 



This nucleus is, of all the masses of the grey floor, the most 

 closely interwoven with fine fasciculi, which for the most part 

 extend from the cerebellar peduncle towards the raphe', and in- 

 close the nerve corpuscles, which have a length of from 30 to 

 45 ju, and a breadth of from 12 to 15 /z. 



2. The external auditory nucleus (Clarke, Dean) embraces 

 the trapezoid area of the internal division of the crus cerebelli, 

 which, applied immediately to the internal auditory nucleus 

 (fig. 255, H, on the left side, behind 8 4 on the right side, 

 fig. 257, SFC), has the anterior and posterior line of demarca- 

 tion in common with it, and is in contact externally with the 

 restiform body of the crus cerebri. The transverse section of the 



