DEVELOPMENT OF THE SKULL IN THE MAMMALTA. 
49 
This somewhat lemurine skull, seen from above (Plate 8, fig. 2), shows in this early 
stage some promise of the stony solidity of the skull of the adult. The roof-bones 
are forming rapidly, and only a lozenge-shaped fontanelle (fo.) remains in the vertex. 
The premaxillaries (px.) are scarcely seen in this aspect; but the facial plate of the 
maxillaries ( mx .), and the great front alveoli, come into view ; between them the 
nasals (n.), behind the short snout ( al.n .), are seen as short, wide bones, only one-third 
longer than broad, and having their fore edge cut away on the inside. The maxillaries 
and nasals form a convex margin to unite with the concave fore margin of the 
frontals ( f ). Outside their narrow fore end the smallish lacrymals rest on the jugal 
process of the maxillaries, and behind these the jugals (j.) come into view. Even 
now, in their narrow fore part, the frontals show that pitting which is a sure sign of a 
dense and solid bone in its early stage. The remainder of these bones is radially 
fibrous, like the parietals (p.), and these plates are about equal, the fore part of the 
frontals being left out of consideration. 
The supraorbital rim is better formed than in the Armadillos ; its terminal or 
postorbital process is well defined. From it, forwards, the edge of the bone has a 
gently concave outline, so that, although the frontals narrow in, forwards, they form 
-everywhere a large roof over the fore brain. The postorbital part of the frontals is 
one-third the extent of the whole, and it nearly reaches as far outwards as the large 
convex parietals (p.). In their re-entering angle, behind, we get a view of the upper 
half of the occipital arch ( s.o .), which is ossified very early and very rapidly; much 
more so than in the Dasypodidse, although in neither of these types is there any 
“ interparietal ” or additional membrane bone, or bones.* 
This cartilage bone shows the pitting, which is seen in the fore part of the frontals. 
The occipital condyles (see, also, fig. 1, oc.c .) can just be seen from above. 
In the side view (fig. 3) we get a display of parts, the figure of which might serve 
as an elementary diagram of a Mammalian skull. The short, depressed snout shows 
* There is something which has to he accounted for, here; the interparietal, which is formed nearly 
always from two primary centres, and which figures so largely in Marsupials and Insectivores, and in the 
Eutheria above them, is totally absent in the Neotropical Edentates, and in the Pangolins of the Old 
World. In Orycteropus it is as large as in the Insectivorous Bhyncocyon from the neighbouring region— 
(Zanzibar, East Coast)—a type, the skull of which I shall compare, in my next paper, with what I am 
able to show of Orycteropus in this; for the Cape Anteater lies somewhere between the Armadillos and 
that most perplexing, most generalized Insectivore. Looking at the Mammalia, generally, and bearing in 
mind that Birds with the largest skulls (Crows and Songsters) have no interparietal, it seems evident 
that that bone comes in to help the parietals in roofing in the enlarging brain of the Mammal. In a 
young Ornithorhynchus, the size of a new born kitten, with the hairs just appearing, the parietals form 
one thick continuous mass, as in the Ophidia, and the large bilobate ossification of the supraoccipital 
cartilage, is fast growing to its hind margin. I see, also, the same thing in the Echidna at a little later 
stage. Some things, no doubt, in the Edentata are due to degeneration, or suppression, but I feel sure 
that they were never higher in the scale of the Mammalia, on the whole, than they are now, and strongly 
suspect that they are a sort of metamorphosed Monotremes, in which the Marsupial stage was got 
through rapidly. 
MDCCCLXX XV. H 
