580 
ME. W. Iv. PAEKEE ON THE STEUCTUEE AND DEVELOPMENT 
surrounded by bone, and appears in Spelerpes as a well walled round by the nasal 
process of the azygous premaxillary. 
In Seironota (figs. 4 & 5, m.n.c.) it is behind the palatal plates of the premaxillaries 
and between the great vomerine blades ( v .). Above, it is seen in the middle of the 
precranial fontanelle. We see that this skull is much like that of a Shark, as to the 
position of the fontanelle and the separation of the nasal roofs. 
As in the larva, so in the adult, the vomers and the palatines are continuous ; but, 
for the same time during the latter part of larval life, they were distinct. The curious 
behaviour of the dentigerous palatine, after it has once become independent of the 
vomer, may be traced in all the higher Urodeles. 
We have seen that in Siredon this bony tooth-bearing plate sent backwards and 
outwards an edentulous process, and that that untoothed part became the larger bone 
by far, and was segmented from the part from which it sprung. 
The same thing has taken place here ; but Seironota agrees with most Caducibranchs 
in having its dentigerous palatine become confluent with the end of the vomer just 
where it has retained a few teeth, and not turned outwards, as in Amblystoma. 
All the fore part of each vomer is now a large toothless blade of bone, forming, with 
its fellow, much of this very strong, hard 'palate , and elegantly notched at its side for 
the inner nostril. 
The sutures on this palate, like the bony plates, are of great extent ; the edges of 
each vomer are denticulated ; but on the whole the vomer is just more than' right-angled, 
where it fits between the premaxillary and maxillary palatine plates. 
Behind the middle nasal canal the left vomer binds strongly on the right ; they both 
then pass insensibly into the long, divaricating, dentigerous palatine. 
Thus we have, from the ethmoidal region to the ear-capsule, a bony tract whose outer 
outline is concave or crescentic ; behind the middle there is nothing but a steep ridge 
of bone bearing teeth. 
These bars reach to the basitemporal angle of the parasphenoid ( pa.s .) ; and if we 
look at the larval skull (figs. 1 & 2) we shall see that these tooth-tracts run along the 
trabecular line even then. 
Whilst giving off the bony pterygoid plate the palatines turned outwards, and then 
loosing themselves from their new segment, a separate osseous “ stolon,” they gradually 
went back to their old position. 
In some Caducibranchs the hinder part of this long rod becomes segmented off, also, 
forming a postpalatine bone. 
The edentulous separated piece, or bony pterygoid (figs. 5 & 6, pg.\ applies itself as 
an ectosteal plate to a process of cartilage which grows forwards from the suspensorium. 
These diverse parts meet and unite, and now in the adult the bony plate has meta- 
morphosed the cartilaginous process ; that process was the quadrato-pterygoid, the 
homologue of the main part of the “ upper jaw ” of a Selachian (that bar ends behind 
in the quadrate). 
