OF THE SKULL IK LEPIDOSTEUS OSSEUS. 
457 
slab does not touch the notochord at this part. These basal bands are quite confluent 
with the auditory capsules, wdiich are very solid on then' outer side, but remain 
membranous to a considerable extent on the inner. 
The anterior semicircular canal ( a.s.c .) is cut through, and also the main cavity (vb.) 
with the horizontal canal opening into it; this canal bulges out the capsule, and 
under the “ tegmen ” thus formed we see the hyomandibular (Jim.) as a continuous 
ray, thick and bulbous, below. Below it, at a little distance, the joint being further 
back, we see the second segment, or inter-hyal (i,hy) ; it is short and semi-elliptical, 
with a truncated end below. That end articulates with the rounded top of the 
phalangiform cerato-hyal ( c.hy .), which is between it and the hypo-hyal; this latter 
segment was in front of this section (see Plate 30, fig. 8, h.hy.) 
The foremost branchial arch is cut through near its ventral end, through the lower 
part of the cerato-branchial, as well as the distil and basal pieces ( c.br ., li.br., b.br.) ; 
these parts lie behind the tongue. 
Section 13.—The next section (Plate 31, fig. 13) is behind the junction of the auditory 
capsules with the basal plates. These latter are here very massive, and almost square; 
the notochord (nc.) between them is very large; the ganglia of the vagus and glosso¬ 
pharyngeal (IX., X.) fill up much of the space below, between these bars and the 
capsules; but above, the open space is for the auditory nerve (VIII.). The anterior 
and posterior canals ( p.s.c .) are cut through at their junction, and the horizontal canal 
where it opens behind into the vestibule (vb.). The hyomandibular (Jim.) is severed 
behind its upper, or articular head, and that is the only part of the hyoid arch which 
comes into view here. The lower part of two of the branchial arches (br.) is cut 
through close above the heart (h.). 
Bony matter is forming in the opercular fold, a growth from the hyoid region, and 
its great size, wrapping over the gill-arches and heart (Ji.), is well shown. 
Section 14.—In this section (Plate 31, fig. 14*), the auditory capsule is seen to 
approach the investing mass (iv.) behind the large membranous deficiency in the inner 
wall. The basal plates cut through are here at their thickest part, and the posterior canal 
(p.s.c.) is most of it seen, as it becomes bulbous below. Here the notochord (nc.) has 
almost its full (spinal) thickness; the hyomandibular is cut through in its hinder 
part, or “ opercular process; ” only the upper part of this section is figured. 
Section 15.—This (Plate 31, fig. 15*), which is behind the ear-capsule, shows that 
the occipital ring is still very incomplete, only the basal and lateral parts (e.o.) being 
developed. The basal cartilage (iv.) is thinning out towards the first vertebra ; the 
pharyngo-branchial of the last functional arch (p.br.) and its gills (br.p.) are displayed ; 
the notochord (nc.) is now full-sized. A comparison of these sections with the upper 
and lower views of the chondrocranium at this stage (Plate 30, figs. 7, 8) will make 
all plain. 
# Fig. 14 is lettered 15, and tig. 15, 14 by mistake. 
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