588 
ME. W. K. PARKER ON THE STRUCTURE DEVELOPMENT 
These are some of the most important of the modifications in the morphology of the 
skull of a Urodele as compared with that of a Batrachian; there are several more, but 
these must suffice for this present summary. 
Last Stage. Skull of adult TJrodeles and Batrachians. 
A reference to the figures in my papers on the Batrachian skull, and to those of 
Amblystoma and Seironota in the present communication, will serve to show at once the 
sharp distinctness between the two types, and yet their general resemblance. 
One great difficulty in comparing them arises from the fact that several of the TJrodeles 
are perennibranchiate, and therefore permanently quasi -larval ; there are no such Batra- 
chians, and one of that group, namely Pip a, is nearly abranchiate. 
Looking at the skulls of adult (Caducibranchiate) Urodeles and Batrachians from the 
surface we see the following differences : — 
The roof-bones remain distinct in the Urodele ; in the Batrachian the frontal and 
parietal of the same side coalesce. 
In the Urodele the nasal is supplemented by an external prefrontal bone, and is 
therefore much smaller. 
The premaxillaries are distinct in the lower and about half the higher Urodeles ; in 
the rest there is an azygous bone with two long nasal processes. 
These bones are constantly distinct in Batrachia, and the nasal processes are short. 
The maxillary grows further backwards along the face in Batrachia than in the Uro- 
deles ; in one of these, namely Amblystoma, there is a small jugal ; in none a quadrato- 
jugal, a constant bone in the Batrachia, binding the cheek to the quadrate. 
There is only one “ temporal bone ” in both kinds, with the exception, again, oi Ambly- 
stoma ; and in the Urodeles this does not so often grow into the postorbital region. 
Beneath, the parasphenoid is much smaller and more specialized in the Batrachia 
than in the Urodeles ; it begins much earlier in the latter, in the Batrachia it develops 
into a dagger with a large basitemporal guard. 
The vomers are double in both, save in Bactylethra ; the palatine base is only trans- 
verse (as in the Batrachians) in some “ Lechriodonts ” ; in most Urodeles of the higher 
kinds it lies under the parasphenoid, and is ankylosed to the much enlarged vomer in 
front ; these are called “ Mecodonts.” 
In both we have the double occipital articulation and the absence of basal and key- 
stone pieces in the occiput. Yet in some larval Caducibranchiate Urodeles two basal 
vertebrae are partly developed and then disappear. 
In most species of both kinds the prootic is large, and the rest of the ear-capsule is 
ossified by an overgrowth from the exoccipital. 
Except in Bactylethra the two wall bones (sphenethmoids) are fused into a girdle by 
the help of superethmoidal bone ; in the Urodeles the later bony tracts run back past the 
optic foramen, but never, or seldom (for example, in Siren lacertina), unite at the mid line. 
In a few Urodeles, namely, Siren lacertina and Salamandra maculosa, there is a short 
