DEVELOPMENT OE THE SKULL IN THE BATRACHIA. 
635 
The subocular fenestra (so.f.) is narrower in front and wider behind ; for now the 
pedicle (pd.) bends a little outwards, and its dorsal end can be better seen below, 
wedging itself in between the trabecula and the auditory capsule, and yet continuous 
with both. By their bending outwards we do get a very obtuse “ elbow ” to the man- 
dibular pier, but this is masked by huge foregrowth of the tegmen ( t.ty .). 
The “ orbitar process ” (or.p.) is wasting, the articular pulley of the quadrate ( q .) is 
now definitely seen in both the upper and lower view (figs. 3 & 4). Also, with greater 
clearness can we now see how the great labial adheres to the upper face of the inter- 
nasal plate and cornua trabeculae ( u.l ., i.n.l ., c.tr.). 
Small granular masses are forming around the nasal sacs, and are bearing new 7 upper 
labials ; there are two pairs above, and two pairs below (figs. 4 & 5, u.l. a , u.l. b , u.l. c , u.l. d ). 
These cartilaginous nuclei will be described in the adult ; the remarkable thing about 
them is that these persistent nostril-valves are not formed by the breaking up of the 
primary, upper labials {u.l.), and therefore they do not correspond with the two pair of 
persistent labials in the Common Frog and Toad (Plate 54). 
The growth of the trabeculae all about the nasal sacs is neater and fuller ; the septum 
nasi (fig. 3) is now chondrified above, whilst its trabecular floor (fig. 4, s.n.l.) is 
narrower and longer. Besides this better setting of the nasal sacs, the cartilage along 
the huge ethmoidal region above (fig. 3, eth.), although translucent and showing the 
olfactory crura (1), yet is now solid. It is the extended counterpart of the little 
bowed wall of the Common Frog’s Tadpole at the same stage (“ Frog’s Skull,” plate v. 
fig. 3, eth. 1). The great fontanelle is exactly roofed over by a large pair of frontals (/*.), 
which are gently convex, and together form an exact ellipse ; stuck on to these, behind, 
are a very small pair of parietals (p.), sharp in front and broad behind ; they overlap 
the frontals largely, and are just free behind. These, with the parasphenoid, are all 
the outer bony tracts I could find in this stage. 
The large flap of the “ tegmen ” almost closes upon the thyroid gland {tr.g.), and 
the long outer lobe, broadening at each end, is becoming more evidently marked off 
from the tegmen, and more crescentic in form, ready to become the “ annulus.” 
The tentacles ( tc .) are one third shorter ; altogether, this stage leads in gently towards 
the further metamorphosis of the large-legged Tadpole (Plate 58. figs. 2, 3). 
Skull of Dactylethra. — Fourth Stage. Young , with large legs and diminishing tail*. 
The meaning of the lesser modifications in the last stage will be plain now that these 
parts are still more metamorphosed. 
The breadth of the hinder half of the skull is twice that of the front half, and the 
auditory capsules and their curtains have added to them the projecting condyles of the 
quadrate, which in the first stage came up to the fore margin (Plate 56. figs. 4. 5, and 
Plate 58. figs. 2, 3, g.). 
The foramen magnum (Plate 58. figs. 2, ?>,f.m.) is now perfectly formed; the noto- 
* See Dr. Okay’s fig. 2, op. cit. 
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