590 
ME. W. K. PAEKEE ON THE STETJCTUEE AND DEVELOPMENT 
capsule as in Mammals. In Dactylethra it is suspended by a ligament ; in Bufo agua 
it is largely, and in Pijga wholly, absorbed. 
The epihyal piece is mostly small in the Batrachia ; it is developed early in Pipa and 
very late in Pufo, Pana, and Dactylethra. 
This small hyo-mandibular element becomes the “ columella auris.” In Toads it has 
two bony centres and an orbicular symplectic end. In Frogs it becomes two distinct 
pieces, and has a spatulate symplectic end (the extrastapedial). 
In the Urodeles the two last branchials are absorbed ; also the second arch becomes 
simple. Sometimes the first ceratobranchial is lost. The first basibranchial becomes 
very large, and the second ossifies behind, and is absorbed in front ; this bony remnant 
becomes a transverse, azygous thyro-hyal; it sometimes is a mere rudiment, and at 
others is totally absorbed in old age. 
In the Batrachia two rudiments of arches remain on the hind part of the side of the 
hyo-branchial lingual plate. 
Their common hypobranchial plates grow further backwards, become terete, ossify, 
and form symmetrical thyro-hyals. 
These are some of the more important morphological differences between the two 
groups. I may mention a histological difference, namely, that the Selachian incrustation 
of the cartilage seen in the Batrachia (not in tesserae , but in large, irregular patches) 
does not occur in the Urodeles. 
At the risk of prolixity, I have thus compared these two groups as to their cranial 
morphology. Much of the work already done has not had time to see the light ; and 
much more will be done, if possible, as no other Vertebrata run through so large and 
instructive a series of metamorphoses, and no other types have such extensive rela- 
tionships. 
I may remark that the Urodeles seem to approximate most to the “ Sauropsida,” and 
the Batrachia to the Mammalia. The largest species are invariably the most gene- 
ralized ; and some of the larger Batrachia, such as Pana pipiens and Bufo agua , have 
many things in them that remind the observer of the “ Labyrinthodonts.” 
The two aglossal Toads, lately described, so extremely unlike in most respects, and 
yet agreeing in being tongueless, suggest most extensive lacunae in the group. The dis- 
crepancies between the larger “ Perennibranchs ” do the same. 
The Amphibia are not studied, however, for their own sakes ; but it is sought to gain 
more and more insight into the meaning of the skull in the Vertebrata generally, and 
not of the skull only, but of the whole skeleton. 
That framework, also, is considered in relation to all the other structures, eminently 
the nervous system ; and thus we seek to have a clear view of a vertebrated creature 
throughout its adult complexity of structure, and also of all the stages through which 
it passes. 
Of late, the invaluable researches of my friend Mr. Balfouk have come in to open up 
more and more the secrets of embryological growth. His memoirs, and the later 
