28 THE VOYAGE OF H.M.S. CHALLENGER. 



from the fold of the mid-braiu (C 2), and a small remnant of the auditory capsule (ou.) is 

 seen just where the columella (co.) fits in. 



Much of the " epipterygoid" {e.pg.) and all the pedicle (pd.) are seen in this slice; over 

 the lower part of the quadi-ate {q.) the tympanic cleft {cl. 1) is seen, and below, the 

 angular part of the lower jaw {ag.) is cut through ; in front of this is the angle of the 

 mouth {m). In this sub-mesial section the roots of glosso-pharyngeal, vagus, and hypo- 

 glossal nerves (9, 10, 12) are well seen, arising from the sides of the thick lower part of 

 the medulla oblongata (C 3). 



In the ninth the fibres pass out near to each other, but. in the tenth there are 

 clearly to be seen five main bundles, and in the twelfth, three. The ninth passes 

 behind the cerato-hyal (c.hy.), and the twelfth is bounded behind by part of the occipital 

 arch (e.o.). 



Seventh Section. — This section (PI. VII. fig. 6) is equivalent to the last, but is seen 

 reversed, the parts seen are the same, on the whole, but some things are better displayed, 

 and some new things come into view. The motor oculi nerve (3) is seen to have a 

 bulbous or ganglionic origin from the sharp fold of the mid-brain (C 2) ; it goes down- 

 wards and forwards, and passing over the post-clinoid wall {jj.cI.) forks, and, according to 

 Milnes Marshall, forms at that point a ganglion. Its main branch is seen in this section 

 to cross the orbito-nasal branch of the fifth (5^) on its inner side, above and behind the 

 entrance of the optic nerve (2), and it is still seen in front of the external rectus 

 muscle. 



Much of the Gasserian ganglion (5) has been cut away with the stem of the 

 second and third branches. Behind that ganglion another, not much less than it, is seen ; 

 this is the ganglion geniculatum {g.gc.) of the seventh and eighth nerves. 



The descending stem or facial nerve has been cut away, but the roots of this segmental 

 nerve are seen to be copious, and to arise from the sides of the base (at this late stage) 

 of the medulla oblongata (C 3), at just under the fold where the mid-brain (C 2) begins. 

 The large oblong ganglion is seen to send down a stolon of fibres which run into another, 

 the ganglion cochleare (g.cl.), see also PL VI. figs. 6, 6a. 



The ninth, tenth, and twelfth nerves (9, 10, 12) are seen as in the last figure, but with 

 a tract of the auditory capsule {cm.) between them and the observer. 



Eighth Section. — This section, so much of it as is figured (figs. 7, 7ct), corresponds with 

 the solid vertical section already described (PI. III. fig. 4) ; it is a little to the left of the 

 middle, so as to show the orbito-nasal septum perfect. The fore-brain (C 1) is giving ofi' a 

 small diverticulum in front (there is one on each side), the rhinencephalon (C lb), but 

 this " olfactory tract " is quite distinct from the sohd olfactory nerve (1) which arises 

 from the fore and upper part of the brain. The optic nerve (2) has been cut through 

 close to the brain ; and the third (3) is seen running down to the post-clinoid wall 

 {p.cL). An azygous bud is growing out of the fore-brain at its posterior region ; this 



