or THE SKULL IN THE UKODELOITS AMPHIBIA. 
587 
The suspensorimn of the Tadpole is of a huge size, and in one kind, that of 
Pseudis parctdocca, reaches by its quadrate condyle to the front of the face. A little 
behind the trabecular band it grows upwards as a large leaf of cartilage that overarches 
the temporal muscle and “ trigeminal ” branches, and in the Toad, as in the Lamprey, 
coalesces with the ethmoid. 
I have not yet found a trace of this structure in any Urodele. 
In the Axolotl the hyoid cornu alters very little from what it was at first ; in the 
Tadpole it retains its massiveness, breadth, and shortness until the gills begin to shrink; 
then it soon becomes a long, narrow tape, loosens itself from the suspensorium, and 
attaches itself to the auditory capsule. 
To the end of the tailed and branchial stage the gill-arches are persistent in the 
Tadpole, but become bands ; in the Axolotl they are massive bars that only alter if the 
Siredon turns into an Amblystoma. 
Up to that time also the pterygoid process of the suspensorium alters but little except 
that it grows larger and adds a separate piece to its apex, a segment comparable to the 
autogenous pharyngobranchials of a Skate. 
But the osseous plates that apply themselves to the cartilage are very different in 
their origin in the two types. 
In the Axolotl the little dentigerous palatine sends a toothless process backwards and 
outwards to the suspensorium ; this then separates, the toothed piece turns outwards in 
Amblystoma , and inwards and backwards under the skull in Caducibranchs, generally. 
In the Batrachian a thin independent toothless bone applies itself to the under surface 
of the ethmopalatine bar, as its ectosteal plate ; and another larger plate applies itself 
to the inner face of the suspensorium, to its pterygoid process, and in Toads to the 
pedicle ; in Frogs there is a separate mesopterygoid applied to that process, and which 
in them becomes large and detached from the trabecula. 
In JBufo agua , under the huge ethmo-palatine ectostosis, a counterpart of the little 
transverse palatine of Amblystoma appears. 
Whilst these things are taking place in the Frog the palato-quadrate band keeps 
lengthening, the gape widening, and consequently the quadrate gets further and further 
backwards, until at last the suspensorium forms an obtuse angle with the basis cranii. 
By the time the tail has disappeared in the Frog the primary otic process has become a 
free trifoliate “spiracular cartilage;” this becomes the cartilaginous “annulus tympa- 
nicus it is always, at any stage, above the portio dura nerve. 
In certain Urodeles, namely Menopoma , Spelerpes, Desrnognatlius, the two latter being 
Caducibranchs, this cartilage grows to the stapes, and generally fits its narrow posterior 
end into a cupped process of the stapedial bony centre ; in some it is independently 
ossified and free. 
These two specializations of that peculiar Selachian cartilage are of great interest, 
suggesting the possibility of many curious transformations of ichthyic elements in the 
higher Classes. 
4 n 2 
