252 
MR. W. K. PARKER ON THE STRUCTURE AND 
This archaic, generalised skull helps us to see how severe, “ in number, weight, and 
measure/’ the morphological law is, that has, at last, reduced the Anurous type of skull 
to the elected simplicity of that of the Common Frog.'"' 
SUMMARY. 
A.— Primitive form of chondrocranium. 
In a Common Frog or Toad, soon after hatching, whilst the true outer (or cutaneous) 
gills are present, cartilage appears in the cephalic region. 
This first endoskeletal framework consists of three sub-parallel bands on each side, 
that converge a little forwards, are some distance apart, and are almost entirely in 
front of the notochord (Phil. Trans., 1876, Plate 55, figs. 1, 2). 
Other cartilages form about the same time, immediately under the skin, as labials in 
front, and as branchial pouches behind ; but these I shall not now describe ; only the 
true endocranial elements. 
The innermost pair of bands, together, form a lyriform structure ; they are the 
largest; by their hind part they embrace the notochord at its apex ; they diverge 
suddenly, enclose a large pyriform space under the fore-brain, converge nearly to 
touching, and then diverge again, as short, broad, decurved horns. 
These are the “trabeculae craniithey are para-chordal, behind, and the rest of 
each bar is pro- chordal: there is no other parachordal cartilage, as yet; the huge 
notochord, which only gradually lessens to its rounded end, has, right and left, two 
pairs of “ muscle-plates ” enclosing it in the cranial region. 
Where the trabeculae are most bent, behind and in front of the eye-ball, there the 
second band is continuous with the trabeculae; by this double conjugation it encloses 
an oval (sub-ocular) space. 
In front, each of these outer bands turns inwards towards the horns of the trabeculae, 
and develops an oval, short, segment, which also turns inwards. This twice-conjugated, 
second bar, is the “ suspensorium ” of the mandible ; the short segment is the mandible 
itself, or the articulo-Meckelian rod. The hinder conjugating part is the “pedicle,” and 
the fore band is the pterygo-palatine rudiment. 
A little behind that rudiment, on its under face, the suspensorium has a broad 
lozenge-shaped cartilage articulated with it—the third band; this is only half as long, 
but twice as broad as the second, and is the lower half of the hyoid arch—the cerato- 
hyal : the upper half, or “epi-hyal,” is not developed until two or three months after 
the transformation of the Tadpole. Opposite the junction of each first and second 
muscle-plate, there is a hollow ball of cartilage, unfinished (membranous) above; these 
* For the description of the skulls of the “ Aglossa”—Nos. 74 and 75 —the reader is referred to my 
former paper (Phil. Trans., 1876, Plates 56-62, pp. 625-665) ; and “Summary,” infra, p. 255. 
