16 
MR. W. K. PARKER ON THE STRUCTURE AND 
I must here remark that the early cranium of the Aglossal types, especially that of 
Dactylethra, is in some respects more Petromyzine than that- of an ordinary Tadpole. 
In some things the chondrocraniam of the Tadpole of Bufo vulgaris comes nearest to 
that of the Lamprey, as in the fusion together of the various plates of cartilage; 
but the skull of the larval Dactylethra comes very near to that of the adult Petromyzon 
in several respects. 
This is seen in the complete fusion of the elements of the branchial skeleton, and in 
the histological condition of those bars and pouches : these are composed, as in the 
extra-branchial basket-work of the Lamprey, of a very light kind of cartilage, with 
large cells and scarcely any intercellular substance : the large amount of superficial 
cartilage shows also the same relationship. 
The Common Toad differs from most of the Opisthoglossa in retaining the primordial 
“pedicle” to the pier of the mandible, which is, from the first, continuous with the 
trabecular bar : this is a remarkable survival of a suctorial character—even after 
metamorphosis. 
SKULL OF LARVAL BATRACHIANS. 
Fi rst Stage.—Craniofacial cartilages of embryo of Bufo vulgaris soon after hatching ; 
\rd of an inch in total length. 
Nearly all the truly cartilaginous part of this cranium (“Skull of Batrachia/' Plate 55, 
figs. 1, 2) lies at the base of the fore half of the head ( tr.); two globes of soft cartilage 
unfinished in their upper third, are to be seen right and left in the hind half: these 
are the very distinct auditory capsules ( au .). 
At present the whole body of the embryo exists as a sort of tail-like appendage to 
the huge and precocious head : the development of cartilage appears, therefore, almost 
entirely in front of the axis of the organism ( notochord ), which stops at the post- 
pituitary space, before the “pituitary body” is formed. 
Thus the cranium, as yet, is nearly all pro-chordal; arid the para- chordal part, like 
the side-walls and roof of the cranium, is still membranous. 
Yet these prochordal tracts, or “trabeculae cranii ” are manifestly true paraxial 
elements or parts; they are homologous with the paired cartilages that appear in any 
region along the sides of the sheath of the notochord. 
All growths above these (dorsad) are of the nature of neural arches; all growths 
below these (ventrad) are “visceral” or “pleural” arches. 
But these rods are continuous , and they are not parallel the one with the other ; 
how is this to be explained on the theory of their paraxial nature ? 
A consideration of the development of this, or of any, Vertebrate embryo, will help 
us to understand the meaning of these first foundations of the cranium. 
The neural axis rapidly enlarges at its cephalic end, forms three vesicles there, the 
hind, mid, and fore brain, and this beaded structure is bent suddenly upon itself so 
