OF THE SKULL IN THE UEODELOUS AMPHIBIA. 
581 
In the Selachians, however, the process is huge and persistent ; in Urodeles it is at 
best a thin wedge, and becomes largely ossified. 
The quadrate {g.) is well ossified, and reaches below to the transverse kidney-shaped 
condyle, which forms the base of the vertical suspensorium. 
This pier is clamped on the inside by the pterygoid bone (pg.), and outside by the 
squamosal ( sq .), a strong, triradiate bone, which, like that of the Frog, grows forwards 
in front of the ear-capsule. 
In the Frog it is free in front ; here it applies its split fore end to the postfrontal 
process, and thus forms a temporal bridge ; below, it resembles the preoperculum of a Fish. 
The lower jaw (Plate 29. figs. 6, 7) is strong and gently arched ; the dentary ( d .) nearly 
reaches to the angle, outside; the dentigerous splenial(sj?.)runs back two thirds the length 
of the jaw ; and the articular cartilage is well embraced by the large articulare (ar.). 
The hyo-branchial series has undergone a curious transformation (see figs. 3 & 8). 
The ceratohyals (fig. 8, c.liy.) are but little altered, except that they are pointed 
below and have lost their hypohyal segment. 
That piece has coalesced with its fellow, and also with the fore end of the first basi- 
branchial ( h.hy ., b.br. 1), giving it an alate and emarginate appearance. 
That bar has become very large, crested above, flat below, and ossified for three fourths 
its extent,, that is to say, up to the attachment of the ventral ends of the first and second 
branchials. 
These two bars ( e.br .) have lost their smaller (distal) piece, the ceratobranchial ; the 
first is a thick rod, and is attached to the bone, behind ; the second is small, is attached 
to the sides of the cartilaginous end of the basal piece, and is partly confluent with the 
large bar in front. 
The second basibranchial has entirely disappeared ; I have found the same state of 
things in an old Newt ( Triton cristatus ) ; in some species there is merely left, here, a 
moss-like growth of cartilage in front of a similar growth of laryngeal origin. 
This loss of independence of the second branchial brings this hyoid apparatus very 
near to that of the Bird, whose so-called “basihyal ” is, in truth, the homologue of the 
first basibranchial of the Ichthyopsida, and its “ urohyal” of the second basibranchial: 
this piece, in the Bird, is often dilated at its end where it lies beneath the larynx ; 
the Cryptobranch Siredon (Plate 27. fig. 5, b.br . 2) foreshadows, accurately, this avian 
structure. 
Of course the so-called paired thyro-hyals or “ cornua maj ora” of the Bird correspond 
to the first branchial arch of an Ichthyopsidan ; each is composed of an epi- and a cerato- 
branchial piece. 
If the figures of Caducibranchiate skulls given in this paper be compared with figures 
of the skulls of the various species of Dinornis*, it will at once be seen how clear a 
prophecy we get in this low group of that generalized bird’s skull. 
* See the invaluable series of papers on these Birds (with their excellent illustrations) by Professor Owen, 
in the Transactions of the Zoological Society. 
