464 
MR, W. K. PARKER OK THE DEVELOPMENT 
capsule. The pharyngeal cavity is open below, for here the great opercular fold is cut 
through ; in it bony plates (op.) are forming; in its upper part the root of the 
symplectic (sy.) is severed, and below that a much larger bar with an ectosteal sheath; 
this is the cerato-hval ( c.hy .); below, the fore part of the heart ( h .) is cut through, 
and above and across it the basal, distal, and cornual elements of one or two of the 
middle branchial arches ( b.br ., h.cr., c.br.). Here the parasphenoid ( pa.s .) is of great 
width, undergirding not only the open basal fontanelle, but the basal plates also. The 
fore part of the Gasserian ganglion (5) is cut through. 
Section 9.—This (Plate 33, fig. 9) is through the widest part of the hind brain (C 3 .), 
and behind the fontanelle, for here we have the hind “ tegmen ( t.cr .), as a thinnish 
layer of roof-cartilage, passing externally into the auditory capsules. At this part 
there is a thick band of cartilage on the inner side, in front of the large “ meatus 
interims.” Here the large ampulla of the anterior canal ( a.s.c .) and the beginning of 
the horizontal canal are exposed, and outside it there is a ledge—tegmen tympani— 
with which the hyomandibular (km. ) is continuous. This is a flat cartilage ; the whole 
of the hyoid pier is relatively small in this type. 
Here the notochord is cut through, where it is enclosed by the broad, fore margin of 
the investing mass (iv.), which thins out, and curves outwards and upwards, to join the 
capsule. The opercular fold (op.) is cut through behind the lower part of the hyoid 
arch, which is projected forwards ; the branchials (hr.) are similar to the last, but 
further back in the series, and the heart (A) is now cut across at its fore part. 
There are several bony plates cut through in this, viz. : parietal, squamosal, 
opercular (op.). 
Section 10.—Here (Plate 33, fig. 10) only the upper or main part is figured ; it shows 
a section of the middle or widest part of the auditory capsule, where the inner wall is 
membranous. The anterior canal (a.s.c.) is cut through close to its junction with the 
posterior, and also the horizontal canal (h.s.c.) with the subdivisions of the vestibule 
(vb.). This section is behind the junction of the capsule with the investing mass ( iv.) } 
and shows the ganglion of the 7th and 8th nerves (VII., VIII.). The flat hyomandibular 
(hm.) is still in section, but behind its articular head; the broad parasphenoid (pa.s.), 
and the outer bony plates, are similar to those of the last section. 
Section 11.—This (Plate 33, fig. 11) shows the hind part of the auditory capsule; 
the whole course of the posterior canal (p.s.c.) is seen through this back wall of 
cartilage. Here the capsules are some distance from the investing mass (iv .); above, 
the roof (t.cr.) has become deficient again, and at this part the hyomandibular (hm.) 
is cut through some distance below the condyle, and in this specimen a film of bone 
is seen investing the cartilage. The large notochord (nc.) has also a sheath of bone, 
and under each basal bar there is a section of the forked hinder part of the para¬ 
sphenoid (pa.s.). One of the branchial arches (? the third) is seen in its whole extent 
(p.br., e.br., c.br.,h.br., b.br.). 
Section 12.—In this section (Plate 33, fig. 12) the occipital arch (e.o.) is cut through a 
