OF THE SKULL IN THE UKODELOUS AMPHIBIA. 
571 
The free arches will be described after the bony plates of the skull. 
The upper surface of the skull is imbricated with four pairs of long, splintery, bony 
plates, and the lower surface is faced with two pairs and an odd one ; these bones are 
the counterparts of the earliest bones in the larvae of higher kinds. 
Above and in front, the premaxillaries (px.) are seen to be almost entirely composed 
of the nasal process, the dentary part being only one third the length of these roofing 
spars, whose hind half covers the apices of the long frontals. These latter bones (/*.) 
are wedges more than half the length of the skull ; their broad interocular part is 
gently convex above. 
The parietals (p.) are of the same length, their fore half wedging in under the 
frontals ; they are still more convex than the frontals, for they form much of both the 
side walls, as well as the roof of the skull (see fig. 8 , f., p., pa.s., tr.). Near the ear- 
capsules they send out the normal angular process ; they rise very gently towards the 
mid line, and their outer superauditory margin is almost straight. Behind, they form an 
arched emargination, parallel with, and slightly in front of, the foramen magnum above. 
Both sides, behind, and the hind margin also, are raised and thickened at the edge. 
Running parallel with and a little outside their outer margin, behind, there runs a pair 
of bones, the squamosals (sq.) ; the fore half of these plates is free of the cranium, and 
runs along the postero-external edge of the suspensorium, with the “habit” of a pre- 
opercular. 
The supratemporal and the preopercular halves of the squamosal are both lanceolate, 
but the upper half is nearly twice as broad as the antero-inferior. The two halves are 
united by a slender middle portion, and are gently bent on each other, the arched 
margin being in front. A little below the middle the concave margin gives off a slender 
process, at an acute angle, half the length of the lower part ; it runs backwards, and is 
bent also a little outwards, and passing over the seventh nerve (7 2 ) is attached to the 
fore edge of the stapes (st.). 
This may be called the “ spiracular process ” of the squamosal ; it exists in rudiment 
in Menopoma, and is above its spiracular cartilage ; in Menobranchus it is almost as 
large as in Proteus (Huxley, l. c.). 
The down-bent part has copied the curve of the suspensorium exactly ; the elegant, 
lanceolate supratemporal part protects the broad cartilaginous zone of the ear-capsule, 
and runs halfway along the epiotic. 
The parasphenoid ( pa.s .) runs but little short of either end of the skull ; in front it 
is wedged between the internasal cartilage and the vomers ( i.n.c ., v.), and behind it has 
gradually broadened until it forms a huge floor, whose slightly extended basitemporal 
angles protect the otic zone, nearly to the fenestra ovalis, on each side ; and then with 
a narrowing margin, five times notched, it underlies and coalesces with the feebly deve- 
loped occipital floor ( eo .). The trabecular rods can just be seen outside the edges of the 
parasphenoid (figs. 3 & 8, pa.s., tr.). 
The vomers ( v .) are dentigerous, they have a single outer row of teeth ; wedging in 
4 l 2 
