46 
PROFESSOR OWEN ON THE EOSSIL MAMMALS OF AUSTRALIA. 
from tlie lower end of the occipital condyles forward to the pterygoid plates or posterior 
aperture of the nares. These “ basioccipito-sphenoidal depressions” are bounded laterally 
by a small tuberosity, by the inner surfaces of the occipito-petrous prominence, and by 
a ridge inclining mesiad to the hind part of the base of the pterygoid plate. 
The basioccipito-sphenoidal part of the “ basis cranii” is 3-| inches in length, and 3 
inches in breadth posteriorly. Its plane forms with that of the “ basis faciei,” or bony 
palate, lengthwise, an angle of 130 J ; the basis cranii sinking, the basis faciei rising, as 
they advance. 
The fore part of the tympano-mastoid ridge (Plate II. fig. 1, 8 , 12 ) appears to form the 
smooth flat hind wall of the articular surface for the mandibular condyle, unless the squa- 
mosal should abut against the mastoid beneath the petrotympanic : the cranial bones of 
this part are evidently modified by original antero-posterior compression. This post- 
glenoid process or wall is 2^ inches transversely, and probably was of great vertical 
extent when entire ; it is directed from within outward and rather forward. The arti- 
cular surface has the same direction, and consists of a hind groove (Plate III. fig. 3, g) 
and a front bar, i. e. it is divided from before backward into a strong convexity and 
a deep concavity; both are slighly concave transversely; in that direction the extent 
of the surface is 3-| inches ; from before backwards it measures 1-J inch. The malar ( 26 ) 
descends to bound the outer part of the articular bar, to which it contributes a share of 
the articular surface. The outer end of the groove opens freely upon the base of the 
zygoma, which it slightly indents ; the inner end is blocked by the descending part of 
the rugged petrosal. 
The palatal part of the premaxillaries (Plate III. fig. 3, 22*) is feebly concave, 1 inch 
5 lines across at the interval between the sockets of i 2 and i 3, then contracting to a 
breadth of 1 inch at the middle of the diastema (ib. d) between the incisors and molars: 
the length of this toothless tract is 2 inches 9 lines in a straight line. It is formed by 
a well-defined ridge gently curved inward until near the socket of the anterior molar, 
which part of the alveolar tract bends abruptly downward, 9 or 10 lines, below the 
ridge (Plate II. fig. 1, 21, d 3). The palate is deep transversely between the right and 
left anterior molars (Plate III. fig. 3, d 3, 21*), their interval in a straight line being 1 inch 
10 lines. As the palate expands its transverse concavity decreases ; its greatest breadth 
between the penultimate molars ( m 2 ) is 2 inches 9 lines. Lengthwise the intermolar part 
of the bony palate (ib. 20*, 21*) is, anteriorly, gently concave, then convex, and again con- 
cave ; it extends about an inch beyond the last molars, is bounded behind by a thick 
low rough ridge, a median forward continuation of which divides the back part of the 
bony palate into two shallow rough depressions or channels leading outwards to behind 
the last alveoli. The bony palate appears to be entire ; its length from the interspace 
of the alveoli of the front incisors (22*) is 11 inches 6 lines, from between the alveoli of 
the front molars to the hind border it is 7 inches 6 lines. 
The huge and extraordinary zygomatic arches (Plates II. & III. 27, 2 s, 21) extend straight 
forward in parallel lines for more than half the length of the entire skull (Plate III. 
