266 
MR. J. L. CLARKE ON THE INTIMATE STRUCTURE OP THE BRAIN. 
grey substance of the restiform body (o), sweep through and around the olivary bodies 
(to), some of them decussating in bundles across the back of the anterior pyramids (y), 
and assisting in forming the commissure of the olivary bodies. 
(5) If we examine a transverse section of the medulla a little higher up, at the point 
of the calamus scriptorius, as in fig. 8, we find that the posterior pyramid (b 1 ) is not only 
thrown somewhat aside, but is a little more flattened, and more overlays the restiform 
body (o), from the grey substance of which it is separated only by a smaller quan- 
tity of white substance, as seen at b" on the right side of the figure, where the dotted 
line indicates its outer boundary. At the same time the grey substance of the restiform 
body (o) has not only increased, but become more irregularly scattered in groups or 
patches through its white substance, as seen on the right side. It will be observed also 
that the spinal-accessory nucleus ( t ) has not only increased in size, but has begun to 
split into two lateral halves, by an antero-posterior fissure, at the bottom of which 
the central canal has still a distinct existence. 
(6) On a level with the middle of the olivary bodies, the vesicular column which gave 
origin to the spinal-accessory nerve now gives origin to the vagus nerve, and may there- 
fore be called the vagal nucleus. As shown in a transverse section (fig. 9 ,g), it is 
much larger than in the preceding figure, and has become completely divided by its 
median fissure into two lateral halves which are thrown widely apart at the floor of 
the fourth ventricle. It will be seen also that the increase in the size of the vagal 
nucleus takes place posteriorly, and apparently at the expense of the inner and under 
part of the posterior pyramid ( b ), upon which it encroaches ; for it is evident that this 
pyramid, the limit of which is indicated by the dotted line (on the right side), is 
smaller here than in fig. 8. At the same time the grey substances of the posterior 
pyramid and restiform bodies have coalesced, the white portion of the restiform body 
which previously separated the two being now filled with its grey substance. 
(7) A transverse section at a somewhat higher level presents the appearances seen on 
the left side of the medulla in fig. 10. Here t' is a section of the hypoglossal nucleus ; 
g is a section of the upper end of the oval nucleus of the vagus nerve (y, fig. 11, Plate 
IX.), separating t' from i, which is a section of the auditory nucleus ; n represents a lon- 
gitudinal fasciculus of fibres of the lateral column between the two horns of g, the vagal 
nucleus ; c’ o is a section of the upper end of the pyriform grey substance of the restiform 
and postpyramidal bodies seen at o, fig. 12, Plate IX., and forming part of the auditory 
nucleus ; and p is a section of the superficial grey substance (g>, fig. 12) of the restiform 
body, covered by arciform fibres, as shown at A, fig. 13, which represents a lateral view 
of the medulla oblongata. 
(8) Having thus briefly described these elementary structures of the medulla oblon- 
gata as they are seen in transverse sections, I will now exhibit them in longitudinal dis- 
sections, and employ, as far as possible, the same letters to indicate the same parts. 
The posterior surface of the medulla oblongata, especially in the neighbourhood of 
the fourth ventricle, presents a greater diversity of appearance, amongst different indi- 
