44 
PROFESSOR OWEN ON THE FOSSIL MAMMALS OF AUSTRALIA. 
sources and localities in the Australian continent, will be duly acknowledged in the 
descriptions of such about to be given; and I propose at once to proceed with 
the results of the examination of the evidences at my command of the cranial structure 
of Nototherium *. 
§ 2. Shull. — The singular shape and proportions of this part of the skeleton will be 
recognized at a glance of Plates II. and III. The occipital region (Plate III. fig. 1) 
represents the upper half of a transverse ellipse, being arched above ; the straight line, or 
section, below is interrupted by the paroccipitals ( 4, 4 ), which descend on each side of the 
condyles ( 2, 2), about 2 inches below the level of the foramen magnum, 0 ; the mastoids 
( s, s) and squamosals (27, 27) bound the region externally. The breadth of the occiput 
at its base is 13 inches, the height at the mid line 7 inches. The surface inclines forward 
(Plate II. fig. 1, 3 ) especially at its mid third (Plate III. figs. 1 & 2, 3 ), but becomes vertical, 
or nearly so, as it arches outward. The surface is broadly undulate transversely, being 
concave at the mid third, convex at the two outer thirds. Nearly the whole of this 
surface is roughened by ridges and insertional impressions of nuchal muscles, the sharpest 
and most prominent of which is the medial vertical one (ib. figs. 1 & 2 , 3), extending 
from near the upper border of the foramen magnum to the transverse ridge bounding 
the occiput superiorly : this ridge describes a low arch transversely ; lengthwise it 
extends toward the upper surface of the cranium, describing an open angle with the trun- 
cate apex forward (ib. fig. 2) The condyles form the lower two thirds of the foramen 
magnum, save at the interval of seven lines between their lower ends (ib. fig. 3 , 2 , 2 ). 
From these they diverge as they rise with a vertical convexity, greatest at the lower 
half of the condyle, and more gradual toward the upper and outer end. The transverse 
convexity is more regular, and affects the hinder, outer, and under parts of the joint. 
The length of each condyle is 2 inches 7 lines, the extreme breadth is 1 inch 3 lines, 
the distance between the upper ends is 4 inches 6 lines. The surface towards the 
foramen is almost flat in the least diameter, gently concave or rather undulating length- 
wise. The plane of the occipital foramen is vertical ; its shape is a full ellipse, with the 
least diameter transverse ; this gives 1 inch 8 lines ; the long diameter is 2 inches. 
A broad groove or channel, directed from below upward and outward, divides the 
condyle from the base of the paroccipital ( 4 ). This broad process inclines forward before it 
descends, its hinder plane being anterior to that of the convex part of the occiput above. 
The obtuse termination of the process is continued, with a curve upward and outward, 
by a thick and rugged ridge into the mastoid process (s), which, with the squamosal, 
bounds the occipital region laterally. The outer margin rises from the mastoid with a 
slight convexity for four inches before curving inward to the upper arch of the occipital 
ridge. A fracture of the outer table on the right side of the occiput exposes the extension 
to this part of the cranial walls of the air-cells continuous with larger cavities in advance. 
* Dr. J. D. Macdonald, R.N., had the opportunity of seeing the remarkable skull which Mr. Isaac had sent 
to Sydney from King’s Creek, and his ‘Notes’ thereon are quoted in my Paper in the ‘Quarterly Journal of 
the Geological Society,’ tom. cit. p. 169. 
