OF THE MARSIPOBRANCH FISHES. 
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ethmo-palatine (e.pa.) is much, less here, because of the large space—the subocular 
fenestra—( s.o.f.), and the orbito-sphenoidal wings (o.s.) are rising and diverging; in 
the hollow between them runs the posterior nasal canal (p.n.c ., outline not figured 
in this section). The post-palatine and pterygoid at their junction form a moderately 
high and thickish band ; inside this, near its top, is the third branch of the trigeminal 
(V 3 .) ; below the oral cavity (to.) is the basi-hyal ( b.hy.). 
18 til Section (Plate 21, fig. 6).—Here we see that the apiculate hind part of 
the nasal capsule (see also Plate 18, fig. 3) grows vertically downwards for some 
extent, and that the walls, which underlaid the capsule to some degree, further 
forwards, have now united to form a perfect floor. The median cartilage is partly 
hard; it does not correspond with the etlimo-septal partition of higher types, but 
with so much of the nasal roofs as are developed downwards, back to back, to 
unite with the true septum. The posterior nasal canal [p.n.c.) is seen in the, 
bottom of the deep cranial trough, whose orbito-sphenoidal walls (o.s.) are high 
and diverge so as to make a wide space for the olfactory lobes (C 16 .), and the curious 
limited partition and floor of the nasal capsule ( na.). Here the ivaist of the skull is 
well pinched in, and the orbits and eye-balls (e.) are large ; large, also, is the shelving 
floor of the orbits, which is cartilage above and below, the intermediate space being 
equal in extent to both of the tracts; the upper is now trabecular (tr.), and the lower 
pterygoid (pg.) ; the space, or suborbital fenestra (s.o.f.), is split into two laminae, 
and between them the 3rd branch of the fifth (V 3 .) passes to the lower and front 
parts of the face. 
The oral lining (to.) has now become five-lobed; below it, we see the vertical 
basi-hyal, and close to it a pair of cartilaginous points—the fore ends of the cerato- 
hyals ( c.hy.) (see also Plate 18, figs. 1, 2, 6, 7). 
19 th Section (Plate 21, fig. 7).—This is through the middle of the eye-balls ( e.), 
behind the nasal capsule, where the olfactory lobes (C 16 .) arise from the fore brain. 
The dura mater ( d.m .) is thick, and still retains the form of the back part of the 
nasal capsule, and below this membrane’s roof we see that the side walls (o.s.), which 
are gently out-turned above, are segmented below their middle, opposite the top of the 
posterior nasal canal (p.n.c.). This is the beginning of the orbito-sphenoidal fenestra 
(o.s.f), which membrane is perforated further backwards for the optic nerve (see 
Plate 18, fig. 5). The subocular flange of the trabecula (tr.) is smaller than in the 
last; the remaining parts are quite similar in both sections (pg., s.o.f, Y°., b.hy., c.hy.). 
20 th Section (Plate 21, fig. 8).—Here the section is through the optic nerves and 
the fore brain (II., see also fig. 9, C 1 .), where the orbito-sphenoidal fenestra (o.s.f) is 
wide. The dura mater (d.m.) is still thickened in the middle of the roof, and the 
orbito-sphenoids (o.s.) now turn in above. The trabecular flange (tr.) is very thin, 
right and left, and so also is the trabecular floor, now behind the intertrabecular 
region. This is the last section figured in which we shall see the posterior nasal canal 
(p.n.c.) fairly lodged inside the cranial cavity. The remaining parts are like what 
