208 MR. W. K. PARKER ON THE STRUCTURE AND 
the size of a mustard-seed, and is no larger directly after it is metamorphosed. I 
mention these things to show how sensitive the Batrachians are to their surroundings; 
how much their transformations are modified by the chances of their life; and also, 
how modifiable these creatures are— Protean in their changeableness. 
The skull at this stage'" (Plate 38, figs. 9, 10) is truly Petromyzine, yet it has a 
modification of the cranial structures not seen in the Lamprey ; viz.: the “ orbitar 
processes.” These parts are free above; but in the Tadpole of Bufo vulgaris (Phil. 
Trans., 1S76 ; Plate 55, fig. 3, between q. and eth.) they are confluent with the 
ethmoid, as Professor Huxley pointed out to me ; suggesting, at the same time, that 
they might be the liomologues of the anterior crus of the Lamprey’s suspensorium : 
we neither of us hold this view, now. 
The chondrocranium of the larval Bufo chilensis (figs. 7, 8) is almost circular; the 
whole length, including the labials, is but little greater than the breadth across the 
subocular arches (sj).) ; here the skull is oblong. 
The cliondrification is nearly perfect, but the lines of union of the various elements 
are all visible, being made up of younger, more elongated, and crowded, cells. From 
the occipital condyles ( oc.e .) to the internal nostrils ( i.n .), the basis-cranii is of nearly 
uniform size; it is then lessened by a notch, on each side, half the size of these passages, 
and gains this breadth again, gradually. The hinder part is, as it were, cut away for 
the ovoidal ear-capsules (cm.) ; the interorbital part is straight-sided in the last and 
pinched in this, and the fore-part is in two diverging bands, with a deep notch 
between them. 
Behind the orbital space, the pedicle of the suspensorium ( sp.) passes into the basal 
plate; in front, the ethmo-palatine bands run into it; behind the ear-capsules the 
basal moieties curve round, to enclose the 9th and 10th nerves (IX., X.). From 
the middle of the inter-auditory space, to the great notch in front, there is a spindle- 
shaped space of new cartilage, leaving the thicker, and older, marginal bands of the 
same size as the free bands in front; these latter are curled over, in the frontal wall, 
pointed, externally, in the last, and blunt in this. 
The basal tracts are as follows 
The investing mass.—This reaches to the mindle of the hind skull, and is sepa¬ 
rated by the cranial notochord ( 'nc .), which is shrinking, and is invested with a thin 
(mesoblastic) layer of long cells, scarcely cartilaginous. The rest of the paired 
cartilages are due to the rapid growth of the trabeculae (tr.), and the free fore parts 
are the “cornua” ( c.tr .). The spindle-shaped, thin, new tract along the middle is 
the first part of the “ intertrabecula” (see fig. 8, i.tr.) ; it is very long and wide. 
A second region of this element is seen from above, in the last (fig. 7), as a short, 
thick wall of cartilage, the rudiment of the perpendicular ethmoid (yp.e.). 
The internasal or fore part of this element is membranous at present in both 
* I have already described the earliest state of the Batrachian chondrocranium (see p. 16) in that of 
Bufo vulgaris. 
