DEVELOPMENT OF THE SKULL IN THE EATRACHIA. 
641 
There was, we saw, however, such a lamina, the first starting-point in the formation 
of the Frog’s girdle-bone ; and it existed when ossification of the actual cartilage had 
barely set in (see “Frog’s Skull,” plate viii. fig. 7, eth. p. 173, stage 9th). In that 
observation I was right as to the bone, but did not fully see that the ossification of the 
underlying cartilage right and left took place independently of, but in consonance with, 
this ectosteal “ superethmoidal ” plate. The fact is that the girdle-bone in the frog is 
formed in the same way as its “ suprascapula,” the outer and inner bony growths being, 
at first, quite independent of each other (“ Shoulder-girdle and Sternum,” plate v. var. 
figs., s.sc., p. 79). In the common Toad and Frog this upper plate soon coalesces 
with the circle of bone which is formed around the ethmoidal region, changing the 
solid cartilage into dense bone (see “ Frog’s Skull,” plate ix. var. figs., eth.). 
In Dactylethra this does not take place; here (Plate 59. figs. 1 & 3, s.eth.) a large 
elegant “ supraethmoidal ” plate lies unattached on the surface of the unossified 
ethmoidal cincture, w T hich in the frog is marked out by being bony, whilst in this type 
it is mapped out very exactly, behind, by the arrest of bony deposit, and in front by 
the presence of the nasal membranes. The overlying “ supraethmoid ” is a common 
bone among Ganoid and Teleostean Fishes (“ Salmon’s Skull,” plate vii. fig. 1, eth.) ; it 
crops up again in Lizards and Struthious Birds. Its form, here, is triradiate — its fore 
ray being an oblong bar overlying the septum nasi, and the hinder part consisting of a 
pair of pointed wings. 
When this bone has been removed (Plate 59. fig. 5) the ethmoidal region of the skull 
shows a transverse, serrated margin. The outer of these serrations are the short, 
prepalatine spikes (pr.pa.); the median projection is the perpendicular ethmoid 
overlying the grooved top of the septum nasi ( s.n .); the intermediate serrae grow 
forwards from the broad junction of the antorbital projection of the ethmoid with the 
ethmopalatine bar (e.pa.). 
Below (fig. 6) the bone of the common sphenoidal trough reaches into the substance 
of the ethmoid, behind ; but its fore part is soft ; and an elegant crescentic thickened 
rim curves round behind the nasal pouches, — very Selachian pouches they are. 
This rim reaches as far as the condyloid boss on the under face of the palatine, and 
the two thickenings together form a sigmoid structure. The postnasal rims pass into 
the narrow hinder part of the feebly alate base of the septum nasi (s.n.), which ends in 
front in three buds of cartilage ; these are the rudiments of the azygous prenasal and 
the alee nasi ( yn ., al.n.). Above (fig. 5) the aliseptal laminae are not more deve- 
loped than the subnasal, below. They have clubbed ends, distinct from the alinasal 
rudiments. 
The cornua trabeculae (fig. 6, c.tr.) are extremely unlike those of the frog and 
toad (Plate 54) ; they are continuous with the great labial pouches in front ( u.l .), and 
with the septum nasi in the middle. These cornua are not seen above (fig. 5), 
being covered by the labial pouch ; but below they are seen, as in the last stage, to be 
tilted plates, with their convex face in front ; they grow outwards and turn backwards, 
mdccclxxvi. 4 u 
