220 
PROFESSOR OWEN ON THE FOSSIL MAMMALS OF AUSTRALIA. 
ramus at an angle of 120°. The vertical diameter of the ramus anterior to the carnassial 
tooth is 1 inch 10 lines; it is the same anterior to the origin of the coronoid plate; and, 
save that the upper border is undulated by the alveolar opening, it runs parallel with the 
lower one. The outer wall swells out to lodge the anterior root of the carnassial, the 
vertical swelling subsiding at the lower fourth of the jaw. The dental canal has two 
small outlets anterior to the swelling. The outer wall becomes slightly concave length- 
wise between the socket of the carnassial and the origin of the coronoid, which is broad 
and thick anteriorly (c), where it divides that concavity from the deeper one behind for 
the insertion of the large crotaphyte muscle (/, figs. 1 & 3, Plate XII.). 
The specimen shows only the fractured base of the coronoid plate, the length of 
which in a straight line is 2 inches 6 lines ; its direction is curved with the convexity 
inwards (fig. 3, c, d) : the fore part, formed by the buttress-like development of the 
outer wall of the ramus ( c ), is 7 lines in thickness; it rapidly decreases to 1^ line, 
and returns to 2^ lines in thickness at the hinder part (d). The osseous tissue at the 
fore part of the coronoid is compact and dense. Toward the hind part is exposed the 
dental canal (fig. 2, d), broken across where it was traversing the base of the coronoid ; 
the canal here is narrow tranversely. A narrow longitudinal groove between the base 
of the inflected part of the “ascending ramus” and the part of the dental canal ( d ) 
exposed by the fracture is continued as a shallow impression with a slight curve down- 
ward and forward, and then straight for a little way, becoming obliterated below the 
vertical parallel of the last molar (m 2). This is the only indication interpretable as a 
“ mylohyoid groove.” 
The course of the fracture at the base of the coronoid from its thick fore part is back- 
ward and downward. The lower border of the ramus forms a thick ridge at the lower 
end of the symphysis, and subsides into a rounded or convex tract, gaining breadth as it 
recedes, and becoming flattened as it expands by the increased production of the angle 
of the jaw (Plate XII. fig. 4, a , a!). The crotaphyte fossa (ib. fig. 1 ,f) is not continued 
forward into the substance of the horizontal ramus, as in Potoroos and Kangaroos. 
The symphysis (ib. fig. 2, r, s ) is sub triangular, the lower and longer side being rather 
convex, the upper side almost straight ; the base, which is turned backward and down- 
ward, is bilobed, the upper lobe, with the convex contour, being the longest. The length 
of the symphysis is 2 inches ; the basal depth is 1 inch 5 lines. The upper part of the 
symphysis forms a slightly concave tract or platform, 9 lines in breadth at the fore and 
inner part of the carnassial, which increases as it recedes, sloping downward and backward 
(ib. fig. 3, s ). It is bounded externally by the sockets of the incisor («) and of the pre- 
molar teeth (p 1-4 ) in continuous series. There is no true diastema between the laniary 
and the carnassial ; the three closely aggregated empty sockets of probably as many single- 
rooted, small, soon shed, functionless premolars occupy the intervening tract and some- 
thing more, viz. by encroaching on the inner side of the fore part of the socket of the car- 
nassial (Plate XII. figs. 2 & o,p 2,p 3 ). Behind the symphysis the inner wall of the ramus 
(fig. 2) is moderately convex vertically, concave in a less degree lengthwise at the lower 
