DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 91 
ascending plate of the palatine (pu.) is seen; it helps the maxillary to form the ant- 
orbital bony wall. 
The hind skull now leans backwards, above ; it is very convex, and has its upper 
and middle part ossified (s.0., e.0.); the exoccipital, a broad band, runs across and then 
downwards behind the crescentic convexity of the opisthotic—which encloses the pos- 
terior canal (p.s.c.)—and the reniform occipital condyle (oc.c.). The articulated 
mandible and the ear-drum hide parts seen in the other side view (fig. 3); the 
annulus (a.ty.) runs inwards and downwards. 
The outer and inner mandibles (here seen from the outside, but shown in their inner 
aspect and more enlarged in Plate 12, fig. 4) are very instructive in this type, at this 
stage. 
Even now the superficial ramus is a very small sinuous bar, with a considerable 
amount of cartilage in its hinder fourth, into which the dentary (d.) runs, ending in 
a point. The condyle (cd.p.) is a convex pyriform tract, lying lengthwise, and with 
the narrow end forwards, it is quite similar to that of the Echidna, but the ramus 
itself (= dentary) is less developed than in that type, although stouter; it has now 
no rudiments, even, of the coronoid and angular processes. 
In this figure (Plate 11, fig. 7) the parts are shown in situ that correspond with 
what we see in the embryo Sauropsidan, the incus or small quadrate (7.) is just seen 
in front of the epihyal (best seen in fig. 8, e.hy.), ander the tegmen tympani; also 
the long internal angular process (m.ml.), with a rudiment of the posterior spur, 
running along the membrana tympani, and Mercket’s cartilage running under and 
within the dentary, which, however, has been made largely out of cartilage.* 
MEcKEL’s cartilage (Plate 12, fig. 4, mk.) is slenderer, relatively, its thickest part, 
now, being near the symphysis; there, meeting with its fellow, it forms a considerable 
basimandibular (figs. 4 and 5, b.mn.). 
As in the Green Turtle (Chelone viridis) the ectosteal articulare (=superficial bony 
centre of malleus), appears first, and the endosteal centre afterwards—in that Reptile 
several years afterwards. The head of the malleal end of the Meckelian rod is solid 
and convex ; the manubrium (m.m/.) is slender and more arcuate than in the early 
embryo (Plate 11, fig. 6), and the lesser posterior process is more indistinct. The 
large incus (7.) and the short, columelliform stapes (s¢.) are unossified, as yet ; the 
* T have never found an “inferior labial’’ cartilage in a Reptile; in Birds, however, it has turned up ; 
in 1843 I found and figured a tract of this kind, of an oblong shape, over the middle of the mandible in 
the Coot (Fulica atra), and twenty years afterwards I dissected out the same thing in another of the 
Rallide, namely, Gallinula chloropus. Now one thing is noticeable in this comparison, and that is that in 
the Sauropsida, as far as I have seen, Mrecket’s cartilage simply shrinks and dies out in the main part 
of the mandible in front of the “articulare,’”’ and does not ossify and become a direct addition to the 
jaw. Nor can I find any actual endosteal ossification of Mucxet’s cartilage in the distal part in the 
Edentates, although the part that is ultimately absorbed directly in front of the malleus (= articulare) 
is separately ossified in the Unau (Plate 9, fig. 7); but in the Insectivora, and even in Man, a large tract 
of Mecket’s cartilage ossifies, and then unites with the ramus. 
N 2 
