PEOFESSOE OWEN ON THE FOSSIL MAMMALS OF AIJSTEALIA. 313 
The upper border of the occipital foramen (Plate XV. fig. 1) is as broad as in the 
Fells spelwa, and broader than in most of the existing species of Lion or Tiger ; it does 
not present the pair of processes that characterize it in those large placental Carnivora. 
As the occiput rises from this border it slopes forward with a slight concave curve to 
the ridge, 3, s (Plate XIII. figs. 1, 3, 8), dmding the occipital from the upper plane of the 
skull : transversely the occiput is concave in the middle and slightly convex on each 
side, with a surface marked by musculo-tendinous insertions ; the median depression is 
partly bisected by a vertical ridge (Plate XV. fig. 1,/), on each side of which there is 
a venous foramen. The breadth of the occiput on the level of the upper border of the 
foramen magnum is 5 inches; its height from the same border 2 inches 2 lines. In 
Fells sj^elma the breadth of this part is 3 inches 4 lines; its height being 2 inches 8 lines. 
The Sarcophlus (Plate XV. fig. 2) much more nearly resembles the TJiylacoleo in its 
low and broad occiput. 
The major part of the basioccipital is broken away (Plate XIV. fig. I) ; the anterior 
portion, which has coalesced with the basisphenoid {ih. 5), forms with it, not a plat- 
form extending horizontally forward, as in placental Carnivora^ but a bent surface form- 
ing a curve convex downward as it extends forward; this character is seen in the Basyuriis 
macriirus and in many Kangaroos; but the convexity at the junction of the basioccipital 
and basisphenoid, 5, appears to have been greater in the Thylacoleo. The base of the 
left occipital condyle, 2, remains ; and in the fossa anterior to it, are the orifices of three 
precondyloid foramina (y), as in the majority oi Marsupialla, including the Basyuri; 
they unite to form a single hole internally in the Thylacoleo. In the placental Carnivora 
the precondyloid canal is single at both ends, and commonly opens externally into the 
jugular foramen {Viverridce, Hyaena, Fells), or close to it, as in the Dog. 
The jugular foramen {i) is bounded behind by a notch in the exoccipital, forming the 
margin turned towards the tympanic, 28 , and which margin is extended further in advance 
of the precondyloid foramina than in the Dog or any placental Carnivore in which those 
foramina do not communicate with the jugulars; in this respect the Basyuri and many 
other marsupials resemble the Thylacoleo. 
The bones composing the complex framework of the organ of hearing are strikingly 
different in the placental and marsupial Carnivora. In the Cat, Dog, Hyana, Civet, 
Otter, Bear, the tympanic bulla is formed by the inflated petrosal with which the true 
tympanic bone has coalesced; in the marsupials the petrosal remains comparatively 
small, and is confined chiefly, if not wholly, to the function of a capsule of the internal 
organ of hearing ; the tympanic bulla is excavated in the inflated base of the alisphenoid ; 
and the tympanic bone itself continues a free and distinct ossicle, which, in the Dasyures 
and Thylacine, is a small thick semicylindrical canal with smooth obtuse margins, and 
its concavity looking backward and upward. 
On the riglit side of the fractured base of the fossil skull in question, the small com- 
pact petrosal (Plate XIV. fig. I, is) is exposed; it is similar to that in the Basyuriis, 
being gioo\ed longitudinally at its inner and under side, the lower border of the groove 
forming a sharp edge, above which, on the inner side of the petrosal, the foramina 
