290 
ME. J. L. CLAEKE ON THE INTIMATE STEUCTUEE OF THE BEAIN. 
nerves. These centres on each side consist of an inner and an outer nucleus. The inner 
nucleus (i, fig. 40, Plate XI.) forms a large convex mass at the surface on each side of the 
fourth ventricle. Lower down in the medulla it arises by a point or angle between the 
pyriform nucleus of the vagus ( g , fig. 11, Plate XI.) and the upper extremity of the pos- 
terior pyramid [V) in the way already described. In transverse section it is triangular, 
one of its angles projecting forward into the root of the caput cornu posterioris, or grey 
tubercle, e, at the side of the slender and longitudinal column, n (see figs. 42, 44, 
Plate XII.). At the lower part of the fourth ventricle it is separated from the hypo- 
glossal nucleus, t' (fig. 11, Plate IX.), by the vagal nucleus (g ) ; but higher up it is con- 
tinuous laterally with the “fasciculus teres,” K' (fig. 40, Plate XI.), the remains of the 
vagal nucleus (H, fig. 42, Plate XII.) having sunk away from between them to a deeper, 
more anterior, and lateral part of the medulla, at the root of the grey tubercle. This 
inner nucleus of the auditory nerve (i) is thickly interspersed with nerve-cells, which are 
round, oval, crescentic, triangular, or otherwise irregular in shape, and of every variety 
in size, the largest being nearly equal to those of the anterior cornu of the spinal cord. 
(37) The outer nucleus of the auditory nerve (d o, fig. 43, Plate XII.) is in contact 
with the outer side of that jus tdescribed. It consists chiefly of the outer and inner grey 
substance or nuclei of the restiform body ( c'o , figs. 20 & 21, Plate IX., and figs. 22 & 23, 
Plate X.), blended together, and with what remains of the posterior pyramid after the 
complete formation of the inner auditory nucleus. This common mass now assumes 
the appearance of a remarkably beautiful network composed of nerve-fibres, and 
enclosing in its meshes a multitude of longitudinal fasciculi, the cut ends of which are 
represented by the dark spots at c'o in fig. 23, Plate X., and fig. 43, Plate XII. The 
manner in which these longitudinal bundles, with the grey substance between them, are 
derived from the restiform and post-pyramidal nuclei, is shown in the longitudinal 
section of the left half of the human medulla (fig. 24, Plate X.), where c'o, at the upper 
part, is seen to be formed out of c', o blended together at o'. The transverse network 
enclosing these longitudinal fibres is composed chiefly of bundles which proceed out of 
the inner auditory nucleus (i, fig. 23, Plate X., and 43, Plate XII.), on the outer side 
of which they form, on leaving it, a beautifully serrated border. The cells are of dif- 
ferent shapes and sizes, but are very much branched, or elongated on the one hand, in 
the direction of the transverse fibres of the network amongst which they lie, and which 
their processes contribute to form ; and on the other hand, in the direction of the lon- 
gitudinal bundles enclosed in its meshes. 
(38) From both of these nuclei (the inner and the outer) the posterior division of 
the auditory nerve takes its origin. Near its exit from the inner nucleus (i, fig. 43, 
Plate XII.) there is generally a gentle swelling or elevation on the surface (i 1 ), which 
contains a number of small cells dispersed amongst its fibres. From this point it 
winds, as a broad convex band (P), outwards and forwards over the restiform body ( p '). 
In this course it contains at first a few small cells, but as it proceeds outward the cells 
become larger, elongated in the dirction of the fibres, and more numerous, until, at the 
