386 PROF. OWEN ON THE OSTEOLOGY 
extent equal with the ex-occipital processes ; they are somewhat compressed laterally, and 
instead of the smooth and polished surface which characterizes them in the preceding 
genera, terminate here in a rough ridge.. The dilated air-chambers or bulle of the 
sphenoid are relatively smaller in the Phalangers and Potoroos than in the Dasyures, 
and they are incomplete posteriorly in the Kangaroo and Wombat. In the Brush Kan- 
garoo the above process from the sphenoid joins the base of the large descending pro- 
cess of the ex-occipital. The pterygoid processes are relatively largest in the Kangaroo, 
Wombat and Koala, and present in each of these species distinct hamular processes. 
In the Potoroo, Kangaroo and Wombat the sphenoid ala combines with the pterygoid 
process to form a large and deep depression, opening externally. In the Kangaroo, 
Dasyures, Koala and Wombat, the great ale of the sphenoid articulate with the parietal 
bones, but by a very small portion in the two latter species; in the Perameles and 
Potoroos the sphenoid ale do not reach the parietals. 
There is little to notice in the parietal bones, except the obliteration of the sagittal 
suture in those species in which a bony crista is developed in the corresponding place ; 
they present a singularly flattened form in the Wombat, in an aged skull of which, and 
in a similar one in the Kangaroo, I observe a like obliteration of the sagittal suture. 
In the Kangaroo, Potoroo, Petaurus, Phalanger and Myrmecobius there is a triangular 
inter-parietal bone. The corresponding bone I find in three pieces in the skull of a 
Wombat. 
The frontal bones are chiefly remarkable for their anterior expansion, and the great 
share which they take in the formation of the nasal cavity. In the Thylacine the part 
of the cranium occupied by the frontal sinuses exceeds in breadth the cerebral cavity, 
from which it is divided by a constriction. 
The coronal suture presents in most of the Marsupials an irregular angular course, 
forming a notch in the frontals on each side, which receives a corresponding triangular 
process of the parietal bones: this form of the suture is least pronounced in the Myr- 
mecobius and Acrobates. A process corresponding to the posterior frontal augments the 
bony boundary of the orbit in the Thylacine, the Ursine Dasyure, and, in a slighter 
degree, in the Virginian Opossum; it is relatively most developed in the skull of the 
Myrmecobius fasciatus, where the orbit is large; but the bony boundary of the orbit is 
not complete in any of the Marsupials. In the Myrmecobius there is a deep notch at 
the middle of the supra-orbital ridge. 
I have found the frontal suture obliterated only in the Virginian Opossum and Petau- 
rists ; and in the latter it is remarkable that the other sutures of the head, as the lamb- 
doidal and sagittal, continue distinct. 
The lachrymal bones vary in their relative size in different Marsupialia. In the Koala 
they extend upon the face about a line beyond the anterior boundary of the orbit, and 
at this part they present a groove, with one large and two or three small perforations. 
In the Wombat their extent upon the face is slightly increased ; it is proportionately 
