OF THE SKULL IN THE UBODELOUS AMPHIBIA. 
547 
It is as though the cartilaginous coat had been filled to bursting, and giving way, a 
crescentic cleft, with its convex edge outwards, was formed, a little mesiad of the under 
surface of the horizontal canal. This space beneath the canal and outside the cleft is 
the first marking off of the “ tegmen tympani.” 
At the back of this morphological rupture, the fast-increasing otolith is seen, partly 
floored by cartilage and partly by membrane ; the cleft itself is the “ fenestra ovalis,” 
opened for the first time in the Vertebrata in this group of the Urodeles. 
The thin ragged inner edge of this natural rent, whose lips have been torn by growth 
and expansion, like the sundering of the leafy rays in the Fan-palm, contains the 
substance out of which a new morphological element, the stapes, will soon be formed — 
an individuated leafy bud. 
Nor is the mandibular pier of less interest than the metamorphosing ear-capsule; it 
is “ laid out and full of meaning,” serving as a key to the modification of this suspensory 
pier right through the air-breathing Ovipara. 
This large cartilage, besides grafting its cartilaginous substance on to the alisphenoidal 
crest of the trabecula, has closely clasped the outer fore edge of the ear-capsule (fig. 4, 
ap., otp., au.). This pedate process ends inwards as a small bud, which, however, grows 
no further in that direction, but stops against the ampulla of the anterior canal ( a.s.c .). 
The lower part of the apex has grown no nearer to the skull, but it has swollen into 
an evident condyle in front of the auditory sac (fig. 5, pd.). 
Thus, the “ pedicle ” in this case is ready to hinge itself upon the prootic region, 
below, as it does after segmentation, when the apex has been absorbed, in the Frog. 
At this stage the otic process exactly corresponds with what is seen in newly curtailed 
Frogs and Toads : in Pseudis paradoxa a like state of things is well seen in individuals 
with the tail reduced to one third its full larval length*. 
The lower part or quadrate region is as narrow as the contiguous part of Meckel’s 
cartilage ; and this latter meets its fellow at the chin, forming a large, bent bow, united 
by the raised points of its equal horns. 
About four pairs of bony plates have been added to the skull and face, besides 
the azygous pieces ; there are now, in all, nine pairs and two median bones. Some of 
these subcutaneous bony deposits are brought into more direct union with the chondro- 
cranium than others, but all are drawn to it as by a morphological affinity. 
The first of the median bones to be noticed is a deposit which ensheaths the apex of 
the notochord, like a rudimentary centrum ; a narrow bridge of cartilage divides this 
little bony cephalostyle from the pituitary body (py.). Under the whole basicranial 
fontanelle, and also extending back beneath the fore half of the notochord and the 
trabecular apices, is the thin submucous parasphenoid ( pa.s .) ; it is lanceolate in shape. 
A film of bone, spatulate above and stalked below, binds down the “ heel ” of the 
otic process, and serves as a splint both to the outer face of the auditory sac and the 
* This triple fixation of the mandibular stem, grafted, socketed, and embracing, is in strong contrast with 
that of the Osseous Fishes, where the simple pedicle is let down to a distance from the skull. 
4 H 2 
