DEVELOPMENT OP THE SKULL OF THE COMMON FKOG. 
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ract of cartilage running from side to side, this view is explained by part of the lower 
view (fig. 8) ; it shows the connexion of the “ mandibular pier ” with anterior part of 
the investing mass ( i.v .). 
The thick outer edge of this bar is the opercular process of the hyo-manclibular ; mesiad 
of that the rest of the nearly horizontal part is the topmost portion of the primary 
mandibular rod, its metapterygoid region. The rapidly ascending part is the “ meta- 
pterygoid connective,” the secondary growth which binds this arch to the investing mass 
behind and to the “ trabecular connective ” (fig. 8, tr.c.) in front. The cartilage on which 
the infundibulum {inf.) rests is the connective or secondary portion of the investing mass 
(fig. 8, i.v.c .) ; this is underlain by the broadening or basitemporal portion of the “ para- 
sphenoid ” {p.a.). 
It must ever be kept in mind that a large triradiate tract of cartilage here, on each 
side, is entirely secondary in its growth, only appearing in the third stage ; the branches 
of this tract may therefore be called the “ connectives” of the trabeculae, metapterygoids, 
and investing mass (fig. 8, tr.c., m.p.g.c., i.v.c.). 
Here the mouth ( m .) is at its widest part, and looking backwards at this front view we 
see the pericardium {p.c.d.) overlain by the “ hypobranchial ” plates {h.br.), which nearly 
meet. Here also parts of the first and second branchial arches {br. 1, hr. 2) are cut 
through, and the rich crop of inner branchial tufts are shown ; the branchial cavity is 
only partly shown, the lower part of the section not being drawn, and the external 
branchial tufts are cut away. 
The next view (Plate V. fig. 7) is a little behind the last ; it is somewhat oblique, and 
catches only a small part of the infundibulum {inf.) beneath the “ mesencephalon ” (C 2) ; 
the “ foramina ovalia ” and the right Gasserian ganglion (5) are shown in this back 
view of a solid section. The fore end of the “investing mass” {iv.) is here seen distinct 
from the auditory capsule on the left side, and from the “ metapterygoid connective ” on 
the right: on this side the auditory sac {pro.) is slightly laid open; but on the left we 
see the ampulla and part of the arch of the “ anterior semicircular canal ” {a.s.c.) : here 
the angular height of the capsule is seen to be due to the arch of this canal. The thin, 
free, hypobranchial horns (figs. 5 & 7, h.br.) are seen investing the pericardial roof {pcd.) ; 
this sac is laid open, and the heart is seen in situ. Part of each of the four branchial 
arches {br. 1-4) appears in this section, and their convergence from before backwards is 
illustrated (see also fig. 5); the external branchial tufts {e.br.) are indicated by outlines: 
the whole of this section is not shown below. 
The next view (Plate VI. fig. 6) is the front of a solid piece still further back; it is 
slightly oblique, and thus the right side of the mouth is seen to be becoming narrower. 
There is a perfect roof of cartilage over the massive “ medulla oblongata ” {s.o., m.ob .) ; 
this is the superoccipital ; for the occipital ring is very obliquely placed, looking forwards. 
The membranous cranium, now serving as perichondrium to the enclosing cartilage, is 
some distance from the cerebral mass, the space being filled with a very watery tissue, 
softer than the subcutaneous stroma. 
