DEVELOPMENT OF THE SKULL IN STURGEONS. 
159 
section, and is twice as large as in fig. 1; the Gasserian ganglion (V.) is here cut through 
behind, and lies within its proper boundaries, namely, with the alisphenoid ( cd.s.) 
above and the investing mass (iv.) below. This section is near the edge of the low 
post-clinoid wall (Plate 14, fig. 4, p.cl.) and the apex of the notochord (nc.), which here 
lies on the gently-scooped plate formed by fusion of the two parachordal bands (iv.). 
The pterygo-quadrate (pg-q. } q.) is cut across close in front of the hinge, above and 
below, for it appears in two parts on account of its curve downwards to form the hinge. 
Meckel's cartilages also (mh.) are cut through close to the hinge; they are placed across, 
behind the mouth, are gently arcuate, and slowly lessen towards the meeting point. 
Outside the hinge, an angle of the symplectic (sy.) has been cut off. 
Section 12.—This section, half of which was drawn (Plate 15, fig. 4) like the last, 
is a front view; here the cavity of the auditory capsule is laid open, with the ampulla 
and part of the arch of the anterior semicircular canal (a.s.c.). The sphenotic cartilage 
is still seen above and below this front part of the capsule; from the capsule to 
the investing mass is the foramen ovale with the ganglion of the 5th (V.), perhaps also 
part of the “ganglion geniculatum,” which belongs to the facial and auditory nerves 
(Plate 14, fig. 4. VII., VIII.) ; the notochord (nc.) still lies on the investing mass (iv.). 
The hinge of the lower jaw is seen from its front face; the rod of the mandible (mh.) 
was in the last section, and this shows the articular region. The quadrate end of 
the pterygo-quadrate (q.c.) is seen in its full size with its orbitar process (or.p.) ; outside 
the hinge the symplectic (sy.) is shown, and the bypo-hyal and half the cerato-hyal 
(h.hy., c.hy), and some of the teeth of the lower lip (t.), towards the mid line. 
Section 13.—In this section (Plate 15, fig. 5) the hind-brain (C 3 .) is becoming 
narrower, and each auditory capsule under the arch of the anterior canal (a.s.c.), is cut 
through so as to expose the ampulla of the horizontal canal (li.s.c.) ; above, there is a 
rudimentary tegmen cranii, continuous with the capsule and the hind part of the 
“sphenotic” tract. At this part the capsule, as is the rule in Fishes, is open towards 
the hind-brain, and in the fissure, below, the “ganglion geniculatum” (VII., VIII.) is 
shown. Here the capsules and the basal plates (iv.) are quite confluent, and the noto¬ 
chord (nc.) divides the latter, lying down between the two halves. The front face of 
this section was figured ; here the massive symplectic (sy.) is shown in its front half, 
and a considerable portion of the cerato-hyal (c.hy) ; the hypo-hyals are lost in this 
section, they were shown in the last (fig. 4) ; the basi-branchial, the first hypo-branchials, 
and part of the first cerato-branchials (ji.br 1 ., c.hr 1 .) are shown here as well as the 
“ protractor hyomandibularis ” muscle (pt., hm). Teeth (t.) are seen as far down, inside 
the throat, as the first hypo-branchials. 
Section 14.—In this section (Plate 15, fig. 6), the hind-brain (C 3 .) is much smaller, 
but the auditory capsules are at their widest part; they are continuous with 
the thickening parachordals, which enclose an enlarging notochord (iv., nc.). Below 
these parts and their underlying vessels, teeth (t.) are still seen. The super-occipital 
tegmen (s.o.) is growing inwards from the edge of the capsules, but these margins of 
the great fontanelle are nowhere closed in (from end to end) at present. 
