316 PEOrESSOE OWEX ON THE EOSSIL ]\LUOIALS OE AHSTEALIA. 
been moulded solely in obedience to the piessme of the enonnous temporal muscles, and 
present a uniform concavity towards the temporal fossae. The cranial waUs here 
(Plate XIII fig. 1, sr) show as little indication of the bram within as m a cold-blooded 
reptile • amongst the mammaUan Carnivora the nylacoleo is unique in this resect ; and 
in the diminutive relative size of its cerebral organ, it is approached only by the Thylacme 
and the largest existing species of Das^aire. 
In the Bas. urdnus the apparent breadth of the cranial chamber is here greater than 
it actually is, by reason of the swelling out of the squamosal above the root of the 
zygoma through the extension therein of tympamc au'-cells; and sii^ai au-cells me 
exposed on the right side of the fossil Thjlacoleo (Plate XI. fig. 1, c) ; but I know o 
no species of placental Carnivore in which the squamosal is so modified. 
Another equally instructive marsupial character is exhibited by the bony outlet o a 
vein (ib. s), which conducts part of the blood from the lateral sinus to the outer and back 
part of the cranium : this venous foramen is situated behind the root of the zygoma and 
above the meatus auditorius in the Thylacine (Plate XII. fig. 2, s) and Dasyui-es. a 
d mdnr diverticular vein is present in certain placental Carnivora, and has its externa 
outlet behind the glenoid cavity and in front of the meatus auditorius, as e. g m the Dog 
and Otter; there is a small venous outlet on the outside of the tympanic bulla m the 
Cat and Hya;na; but in no placental Carnivore is such a venous foramen present behind, 
or piercing the ridge continued backward from the root of, the zygoma. 
In the Thylaeoleo this venous foramen (s) is present in nearly the same ream e 
position as in the marsupial Carnivora, posterior, viz., to the commencement o t le rmge 
or hind root of the zygoma ; in the Dasyure it is below the upper margin of the ridge . 
in the Thylacine it is posterior to the beginning of the ridge; m the Thylacoho it is 
posterior and superior to the beginning of the ridge. Thus in the same degree m whiri, 
the Thylaeoleo departs in this particular from the largest existing maisiipu aiiinoia. 
it differs from the placental Carnivora, in aU of which the foramen, besides its otiier 
differences of position, is quite below the zygomatic ridge in question. 
The interorbital part of the upper surface of the cranium (Plate XI . g. y ^ 
remarkable in the marsupial Carnivora for its great breadth, especially as compared mtli 
that of the cerebral portion of the cranium ; the transverse diameter of this part a. t..e 
middle and highest part of the upper border of the squamosals is, ui the avyiino 
ursinus, less than half the same diameter of the narrowest part of the iiiterorbhal portion 
of the cranium. In the Tiger, Lion, and Fells sg,elaa the diameter of the iiiteroibi tal 
space is one-seventh less than that of the cranium of the Thylaeoleo, taken acioss it 
same part as in the Basperns. In the Thylaeoleo the least diameter of the » j 
surface is 2 inches 10 lines; the diameter oniie cranium opposite the middle ot 
uuuer border of the squamosals, 27 ', is 1 inch 3 lines. „ , 
The broad interorbital platform of the TIvylaeoleo, with a broad and shallow depression 
and two slight lateral convexities at its anterior half, passing posteriorly into an almos 
flattened surface, decreasing to the point where the temporal ridges [t) meet above 
