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



ate do with the front of the wall on each side of the pituitary recess. The internal 

 carotid arteries (i.e.) are seen ascending on each side in this recess, and behind the wall 

 the basilar artery (b.a.) is seen, with its side branches. The post-clinoid wall {p.cl.) is 

 elegantly sinuous in adaptation to the pituitary body in front, and the ascending part of 

 the hind-brain behind. 



Fourth Section. — In this slice (PI. VIII. fig. 4) both the nostrils and the general 

 nasal cavity are seen on each side of the thin septum {s.n.), which is composed of the 

 " intertrabecula " only. 



The orbito-sphenoids (o.s.) are cut away so as to expose the middle (intertrabecular) 

 plate (i.tr.), and the part of the lowered orbital septum is seen over which the optic 

 nerves (2) pass. Only the stem or narrow part of the alisphenoid (al.s.) is seen at this 

 level ; the top of the common optic passage (2), and of the foramina ovalia (5) are 

 seen ; and part of the Gasserian ganglion and of the ophthalmic (orbito-nasal) nerve, 

 right and left. 



Fifth Section. — Here (PI. VIII. fig. 5) the eyeballs are shown as fairly cut through the 

 middle, for the optic nerves are seen entering the cavity and becoming the retina 

 {e., 2, rt.). The nostrils (e.n.) are laid open, and at this part the nasal wall [al.sp.) is 

 shown separate in the substance of the fore face. This section is very important, for it 

 shows the single nature of the septum nasi {s.n.), and that the orbital region of the 

 cranio-facial wall is triple {tr.,i.tr.). This wall is narrowed below the common optic 

 passage, and is dilated largely behind. The concave hinder margin bounding the 

 pituitary space, with its sections of the lobulate pituitary body {p>y-), is concave, and 

 therefore the intertrabecula is shorter behind than the trabeculse (i.tr.,tr.). 



■ At this level the foramina ovalia are at their widest, and in them lie the large 

 Gasserian ganglia (5), whose roots are seen to be coming from their origin in the 

 medulla oblongata ; their main mass of outgoing fibres form the stem of the second and 

 third branches. 



The boundaries of these foramina are the post-clinoid wall in front, and the ear- 

 capsule {au.) behind ; the former is straighter down here than above, the latter is so cut 

 as to show the arch of the anterior canal (a.s.c). 



Sixth Section. — Only the hind half of this section is figured (PL Vlll. figs. 6, 6a) ; 

 it spans a stratum very little lower than the last, for the Gasserian ganglion (5) is still 

 seen. This is the most instructive of all these horizontal sections, because of the hght 

 which it sheds on the formation of the chondrocranium. Here the narrow hind part of 

 the intertrabecula is wedged in between the broad hind part of the trabeculse {i.tr.,tr.) 

 which are seen to articulate with the post-clinoid wall (p.cl.) by sinuous condyles. 



The internal carotids and basilar artery (i.c.,b.a.), besides other branches, are cut 

 through, but that which is of most importance is that here the notochord (nc.) is so bent 

 upon itself as to appear twice in this section, both times imbedded in the post-clinoid 



