DEVELOPMENT OF THE SKULL IN THE LACERTILIA. 
631 
and squamosals, although feeble, are all of a similar form to what is seen in the adult 
(Plate 41, figs. 1-3; and Plate 42, figs. 1-3). 
The same may be said of those palatine splints, the vomers, and parasphenoid (fig. 2, 
v., pa.s .); and in the nasal passage the septo-maxillaries (Plate 40, fig. 7, s.mx.) have 
appeared as lids to the capsule of the nasal gland (n.g.). The five splints of the 
mandible (Plate 41, fig. 3) are all present and well developed. 
But the “ chondrocranium ” and the endo skeletal membrane bones are well worthy 
of observation, and help greatly to the understanding of the skull in the adult. 
The prefrontal (p.f.) or ecto-ethmoid is here a mere membrane bone, although repre¬ 
sented by an ectostosis in osseous Fishes ; the same may be said of the palatines (pcc.) ; 
the transpalatines, and pterygoids (Plate 41, figs. 1-3, t.pa.,pg.) are well developed. 
All the remaining bony centres are actually grafted on to the substance of the 
chondrocranium, and are effecting its ossification. 
Nearly all these are already present; I miss only two on each side, namely, the 
shaft of the alisphenoicl, and the shaft of the auditory “ columella.” 
Moreover, there are no ankylosed centres; they are all separated, even the most 
advanced, by wide tracts of cartilage. On the floor, the basioccipital (Plate 41, fig. 2, 
b.o.) is separated from the basisphenoid ( b.s .) by the very large, transversely oval, 
“posterior basicranial fontanelle ” ( p.b.c.f. ) and by cartilage outside this space right 
and left. 
Laterally, this half-ring of bone is joined to its side plates, the exoccipitals (e.o.), by 
synchondrosis, so also they are to the upper piece, or superoccipital (Plate 41, figs. 1, 5, 6, 
e.o., s.o.). This latter part is continued forwards as an angular tongue of cartilage over 
the roof (fig. 6, s.o.). 
Within, on the outside, and above, the periotic triradiate suture can be seen as a wide 
tract of cartilage between the three bones (pro., ep., op) ; and the front ray runs for¬ 
wards, being continued along the edge of the side wall of the skull to the front of the 
orbital region (Plate 41, fig. 5). 
For here the massive cranial box of the Selachian is exchanged for a light wicker¬ 
work basket ; and the whole skull, in front of the ears, is a mere grating of cartilage, 
feebly ossified in some parts in the adult. 
But not at present. Now the space between the eyes and ears is largely mem¬ 
branous, full of “ fenestrse,” and framed with ascending and transverse bands of 
cartilage. 
© 
The upper transverse band of the alisphenoid (Plate 41, fig. 5, al.s.) runs from the 
upper periotic dividing line to the postero-superior angle of the orbito-sphenoid (o.s.) ; 
the lower transverse band runs from the prootic to the presphenoid ( p.s .), and behind, 
runs as a descending bar to finish the “ foramen ovale”' (Y). 
Behind the large optic “fenestra” (II) the main ascending bar rises; it is tied to the 
presphenoid by the out-turned fore part of the lower longitudinal band. In the adult, 
up to this point, it is ossified, but not now. 
MDC'CCLXXIX. 4 M 
