308 ME. J. L. CLAEKE ON THE INTIMATE STEUCTUEE OF THE BEAIN; 
fibres very much resembles that of the inferior olivary body. Notwithstanding, however, 
the resemblance of this nucleus, in form and structure, to the olivary body, its position 
is different, being situated behind the trapezium ; while the lower olivary body in Mam- 
malia is behind the anterior pyramid'*. The trapezium consists, for the most part, of 
transverse bundles, which are partially separated from each other by flat longitudinal 
bundles of the antero-lateral column. These transverse bundles ( p'p ", fig. 61, Plate 
XI Y.) proceed, as arciform fibres, from the restiform body on each side, and from the 
remains of the outer auditory nucleus. They sweep round the front of the grey 
tubercle ( e ), then cross the facial nerve (q") , and run inward, in front of the upper 
olivary body (s"), to the back of the anterior pyramid (y), where they decussate across 
the raphe with their fellows of the opposite side. Dean states that many separate 
bundles turn off and curve quite around the nucleus, “ either penetrating its interior or 
completely surrounding it, till the upper side is reached, where the bundle frequently 
turns still more and enters the central portion of the mass, radiating in the same manner 
as the bundles which enter the convolutions in the lamina of the human olivaries”f. 
(69) The prominence of the trapezium at the surface of the medulla is proportionate 
to the development of the nucleus within. In the Cat it projects on each side of the 
anterior pyramid as a large convex and somewhat oval mass J. In the Dog, the Sheep 
and other Ruminants, it is less prominent, and appears as a flattened band in the same 
situation. It is present in all the Quadrumana, but although it varies in size in different 
species, it is generally small, and, in strong contrast to that of the Cat, is sunk deeply in 
the fossa at the outer side of the pyramid. Fig. 62, Plate XIV. represents a transverse 
section of the left lateral half of the medulla of the Orang Outang, on a level with the 
facial nerves. When compared with that of the Rabbit (fig. 61, Plate XIV.) we find 
that the anterior pyramid (y) is enormously developed, and that the trapezium (p") is 
sunk between it and the facial nerve ( q "). Behind the transverse fibres of the trapezium 
the lamina of the superior olivary body (s") appears in the form of a simple loop or fold, 
overlaid, on its outer side, by the group of large multipolar cells constituting the nucleus 
(U) of the motor root of the trigeminus. On each side of the raphe the decussating 
fibres of the trapezium are thickly interspersed with small cells in irregular groups, one 
of which extends forward in a tapering form along the inner side of the pyramid. The 
surface also of the pyramid is covered with a thick layer of small cells (y r ), which extends 
backward along the inner edge of the raphe, as far as the level of the decussating fibres 
of the trapezium. Nothing of the kind is found in the Rabbit, or in any of the Mam- 
malia. 
(70) Fig. 63, Plate XIV. represents a transverse section of the left side of the human 
pons Varolii, at the same level, and magnified to the same extent as’ figs. 61 & 62. 
After examining the trapezium, first in the Rabbit and then in the Orang Outang, it 
will not be difficult to recognize the same structure in Man. As usual, it lies partly 
* “ Medulla Oblongata,” Philosophical Transactions, 1858. + Dean, Medulla Oblongata, p. 64. 
£ See my “ Medulla Oblongata,” Philosophical Transactions, 1858, fig. 4, Plate XII. 
