r from the
palato-pterygoid to the otic capsule is called the quadrate, and at the
point of junction, at the postero-ventral angle of the palato-pterygoid,
articulates with the cartilaginous bar which is destined to form the
substratum of the lower jaw-- Meckel's cartilage (M.c. in Figure 8,I.).

Section 26. Figure 2 shows a dorsal view of these structures in a
young frog. The parts corresponding to these in 1,II. will be easily
made out, but now ossification has set in at various points of this
cartilaginous cranium. In front of the otic capsule is the paired
pro-otic bone (p.o.); behind it at the sides of the parachordal ring is
the paired ex-occipital (e.o.); in front of the cranium box, and behind
the nasal capsules, is a ring of bone, the (median, but originally
paired) sphenethmoid (s.e.). -A paired ossification appears in the
palato-pterygoid cartilage the pterygoid bone (pt.), while- A splint of
bone, the quadrato-jugal, appears at the angle of articulation with the
lower jaw. These are all the cartilage bones that appear in the cranium
and upper jaw of the frog.

Section 27. But another series of bones, developed first chiefly in
dermal connective tissue, and coming to plate over the cranium of
cartilage, are not shown in Figure 2. They are, however, in Figure 3.
These membrane bones are: along the dorsal middle line, the
parieto-frontals (p.f.), originally two pairs of bones which fuse in
development, and the nasals (na.). Round the edge of the jaw, and
bearing the teeth, are pre-maxillae (p.m.), and maxillae (mx.), and
overlying the quadrate cartilage and lateral to the otic capsules are
the T-shaped squamosal bones (sq.). In the ventral view of the skull
(Figure 4) we see a pair of vomers (vo.) bearing teeth, a pair of
palatines (pal.), [and a pair of pterygoids (pt.)] (which [palatines and
pterygoids, we may note,] unlike those of the rabbit, are -stated to be-
membrane bones), and a great median dagger-shaped para-sphenoid
(p.sp.). These two Figures, and 5, which shows the same bones in
side view, should be carefully mastered before the student proceeds
with this chapter. The cartilage bones are distinguished from
membrane bones by cross-shading.

Section 28. Turning now to Figure 8,I., we have a side view of a
tadpole's skull. On the ventral side of the head is a series of vertical
cartilaginous bars, the visceral arches supporting the walls of the
tadpole's gill slits. The first of these is call