DEVELOPMENT OE THE SKULL IN THE BATEACHIA. 
637 
We saw that as we came up, step by step, the large labial ribbon became more distinct 
from the cornua trabeculae. Now, in this stage, it has become two, and each moiety is 
also tilted up in front of the nasal cavity, like the trabecular cornu. Whilst the long ten- 
tacle has been diminishing this change has taken place, and it has become expanded into 
a pouch or “ sling,” which lies more over the upper than the lower surface. The point 
of this corded sling is the anterior valvular plate of the external nostril ( e.n .), which in the 
Frog and Toad (Plate 54) was merely two thirds of each lateral labial piece. Besides these 
two there are three or four pair besides, as we saw in the third stage (Plate 57. fig. 4), but 
the third pair ( ul. c ) escaped my observation in this stage ; they are well seen in the adult 
(Plate 59)*. Above (fig. 2), there is one pair over the edges of the septum nasi and 
another pair attached to the valvular fold behind the outer nostril ( nl . a , nl. b , e.n.). Below, 
the outer pair ( ul. d ) lie in the folds that envalve the inner nostril (i.n.) ; these are large and 
somewhat trilobate : in the adult we shall see their homological meaning. Different as all 
this is from what takes place in the ordinary kinds, it is consonant with the generally 
unusual conditions of this type. The upper ethmoidal region (fig. 2, etli.) is still an 
unwonted structure. All the broad part of cartilage which extends from the frontal 
roof of the fontanelle (f.) to the nasal septum, merely corresponds, morphologically, with 
the cribriform plate and its cartilaginous setting in a young Mammal (“ Pig’s Skull,” 
plate xxxiv. fig. 6, and plate xxxv. fig. 4, cr.l., al.e.); and the pair of tubular passages, 
here, correspond to the many pairs of passages in the higher type. 
The perpendicular ethmoid passes insensibly into the septum nasi now ; the space 
between the olfactory crura (1) is much greater than the thickness of that partition 
wall. There comes out in this stage a process on the antorbital (palato- trabecular 
region), which is not definite in the earlier stages. In the Frog (“ Frog’s Skull,” see 
plate v. fig. 3, and plate vi. fig. 3, inside or.]).) it helps the “ orbitar process ” to enclose 
the temporal muscle, but in the Toad (Plate 55. fig. 3) we saw that the two processes 
were united into a perfect bridge. 
Since the last stage the condyle of the quadrate (q.) has retreated backwards a 
distance equal to one third the length of the entire skull; from being opposite the 
middle of the septum nasi, it is now opposite the fore margin of the frontal hone. 
Still being, like the trabeculse, of great width, the intervening subocular fenestra ( so.f '.) 
is still a mere chink. Below (fig. 3, jod.), the pedicle is seen at its narrowest, where it 
is fused with the trabecula ; from that point it spreads into a huge leaf of cartilage, 
which spreads outwards as far as the crescentic “ annulus ” ( a.t .). But here we see that 
the once continuous cartilage in front of the auditory capsule has become divided into 
three distinct morphological structures. 
The mandibular pier and the foliaceous tegmen (t.ty.) are quite sundered, and from 
the latter the annulus is detaching itself. The “ elbow ” of the mandibular pier, so 
striking a character in all the ordinary Batrachia, now, for the first time, is evident ; it is 
no great distance behind the condyle, and runs by an almost transverse, sinuous edge 
* The third pair ( u.l. c ) are probably not distinct, but are the “ prorbinal ” growths of the trabeculae. 
