ME. J. L. CLARKE ON THE INTIMATE STEHCTUEE OE THE BRAIN. 271 
and in the form of an uncircumscribed group of cells ( t ') ; while the nucleus (t"), which 
now gives origin to the lowest roots of the glossopharyngeal nerve, instead of to the 
upper roots of the vagus, has been pushed, as it were, further outward, the bundles of 
the small longitudinal column ( n ) being now at the outer end of this nucleus, and sepa- 
rating the fibres of the nerve at their point of entrance. The posterior pyramid as a 
separate structure has wholly disappeared, while the triangular mass i , whose cells have 
been enlarging, is likewise increased in dimensions ; and d o of fig. 22 (the outer and 
inner nuclei of the restiform body) have now completely coalesced to form a beautiful 
network of cells and fibres (d o), enclosing in its meshes longitudinal bundles of different 
shapes and sizes, and overlying, as in fig. 22, the extremity of the caput cornu poste- 
rioris (e e), through which transverse arciform fibres are sent across to the raphe to 
decussate with their fellows of the opposite side. Now the former of these two struc- 
tures (i) gives origin (as I shall presently show) to the posterior root of the auditory 
nerve, and I have therefore termed it the posterior or inner auditory nucleus ; while 
the latter (do) gives origin to the other division of the auditory nerve which passes 
underneath, or in front of the restiform body, and I have therefore termed it the anterior 
or outer auditory nucleus. 
(12) By referring, then, to figs. 16, 17, 18, 19, 20, & 21, Plate IX. we find that (1°) 
the chief portion of the posterior pyramid with its grey substance, b', (2°) a large portion 
of the restiform body ( e ) with its grey substance (o) arising out of the posterior part of 
the cervix cornu posterioris (see especially figs. 17 & 18), and (3°) the posterior part of 
the central grey substance (t) which lies immediately beneath the pyramids, which 
gives origin to the grey substance of the pyramids, and which subsequently becomes 
itself the posterior part of the spinal-accessory and vagal nuclei (t t, figs. 20 & 21), are 
all by the histological and morphological changes above described transformed into the 
central organs of hearing, to say nothing at present of the similar relations of these 
to other parts of the brain. 
Fig. 24, Plate X. is a longitudinal and horizontal section of the left half of the 
posterior part of the human medulla oblongata, presenting another view of the anato- 
mical relations of the posterior pyramid, the restiform body, the vagal nucleus, and the 
auditory nucleus. At the lower end of the figure the section corresponds to the trans- 
verse horizontal line b" b" in fig. 6, Plate VIII., much below the point of the calamus 
scriptorius. V is the grey substance of the pyramid, b is its white substance. Higher 
up the section takes off the surfaces of the inner and outer restiform nuclei (o d), the 
former being still separated from the grey substance of the pyramid by its white sub- 
stance (b). A little above this point the white substance of the posterior pyramid is 
lost, its grey substance being fused with that of the restiform body. At o' the section 
corresponds very nearly to the transverse line b" b" in fig. 9, Plate VIII., running 
through the middle of the vagal nucleus (g). Here the vagal nucleus has swollen into 
a large oval or pyriform body, while the posterior pyramid is much narrower and still 
more closely blended with the grey substance of the restiform body. Out of this united 
mdccclxviii. 2 Q 
