PROFESSOR OAVEN ON THE FOSSIL MAMMALS OF AUSTRALIA. 313 



The upper border of the occipital foramen (Plate XV. fig. 1) is as broad as in the 

 Felis spelcea, 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, 8 (Plate XIII. figs. 1, 8, 8), dividing 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 

 Felis spelcea the breadth of this part is 3 inches 4 lines ; its height being 2 inches 8 lines. 

 The 8arcoj)Mlus (Plate XV. fig. 2) much more nearly resembles the Tkylacoleo in its 

 low and broad occiput. 



The major part of the basioccipital is broken away (Plate XIV. fig. 1) ; 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 Dasf/urns 

 macrurus 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 [g), as in the majority of Marsuinalia, including the Dasyuri; 

 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 (Vivenidce, Hycena, Felis), 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 w^hich those 

 foramina do not communicate with the jugulars; in this respect the Dasyuri 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, Hysena, 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 upw ard. 



On the right side of the fractured base of the fossil skull in question, the small com- 

 pact petrosal (Plate XIV. fig. 1, le) is exposed; it is similar to that in the Basyurus. 

 being grooved 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 



