DEVELOPMENT OF THE SKULL IN THE CROCODILIA. 287 
notched behind, and has two rounded notches antero-externally; there is but little 
evidence of a hypohyal rudiment, except the dilated sides of the plate in front of 
the “first ceratobranchials” or thyrohyals (¢.47'); these latter are inbent rods, largely 
ossified. 
c. Investing Bones. 
These were worked out in the largest embryos of the Alligator (Pls. LXVI., LXVIL) ; 
they are already very characteristic of the type, and are much in advance of what has 
been described in the third stage. The main fontanelle (Pl. LXVI. figs. 1 & 4, fo) is 
very large as yet; the parietals (p), only flank its sides as small ear-shaped plates ; they 
have a projecting angle inwards, and look like squamosals. The frontals (/') form a 
sort of “beading” round the large orbits; the upper part is a narrow, crescentic band, 
gently widening from behind forwards. The largest part is the concave orbital flange, 
turned inwards along the whole length of the bone. The frontals overlap the parietals 
behind, and are overlapped by the prefrontals in front. 
The latter bones (p,f) are convex and ear-shaped, with a scooped hind face against 
the eyeball in front; the two are their own width apart on the top of the head. 
In front of these are the nasals (n); they are almost oblong, but are narrow in front ; 
they have a concave fore margin obliquely fitted to the ale nasi (a/.), and are pointed 
‘there at their inner edge. 
The premaxillaries (px) form together a semicircle, broken in the middle, where 
there is a gap between them, showing the prenasal cartilage (p.m); these and the 
maxillaries have a double wall, a deep common alveolar groove, and fast-growing 
teeth in it. 
On each side of the alveolar groove the maxillaries (ma) are well developed both 
externally and within; in the former region there is a large facial plate running from 
the premaxillary in front to a line below the optic nerve (11) behind; this suborbital 
part is narrow, scooped above, and pointed at the end. The palatine edge of the 
premaxillary is small, that of the maxillary is a large ingrowing plate, widest in the 
middle, but half its own width from its fellow. Between the maxillary and the 
prefrontal there is a small triangular bone applied to the lacrymal involution ; this is 
the lacrymal bone (/). Close behind it there is a styloid bone, curved upwards in 
front, downwards behind, and having at its hinder third an ascending triangular 
process; this is the jugal (j). A similar process comes down from a bone above, 
finishing the postorbital rim; this is from the postorbital bone (p.od), the upper part 
of which is a crescentic shell with an outer and an inner toothed process. The relation 
of the postorbital to the parietal is antero-external; it clamps the frontal, parietal, 
jugal, and squamosal. The latter bone (sq) is a large convex trowel, with its “handle,” 
in front, overlapped by the postorbital. 
These two bones are separated from the skull-wall by a deep chink—the temporal 
space; but, behind, the squamosal strongly clamps the auditory capsule, and by its 
you. X1.—Part 1x. No. 4.—October, 1883. 2Y 
