316 



PEOFESSOR OWEN ON THE FOSSIL MAIVOIALS OF AUSTEALIA. 



been moulded solely in obedience to the pressure of the enormous temporal muscles, and 

 present a uniform conca\ity towards the temporal fossae. The cranial walls here 

 (Plate XIII. fig. 1, 27') show as little indication of the brain within as in a cold-blooded 

 reptile : amongst the mammalian Carnivora the ThylacoJeo is unique in this respect ; and 

 in the diminutive relative size of its cerebral organ, it is approached only by the Thylacine 

 and the largest existing species of Dasyure. 



In the Das. iirsinus 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 tympanic air-cells ; and similar air-cells are 

 exposed on the right side of the fossil Thylacoleo (Plate XI. fig. 1, c) ; but I know of 

 no species of placental Carnivore in which the squamosal is so modified. 



Another equally instructive marsupial character is exhibited by the bony outlet of 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 Dasyures. A 

 similar diverticular vein is present m certain placental Carnivora, and has its external 

 outlet behind the glenoid cavity and in front of the meatus auditorius, as e. g. in the Dog 

 and Otter ; there is a small venous outlet on the outside of the tympanic bulla in the 

 Cat and Hysena ; 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 Thylacoleo this venous foramen (s) is present in nearly the same relative 

 position as in the marsupial Carnivora, posterior, viz., to the commencement of the ridge 

 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; in the Thylacoleo it is 

 posterior and superior to the beginning of the ridge. Thus in the same degree in which 

 the Thylacoleo departs in this particular from the largest existing marsupial Carnivora, 

 it differs from the placental Carnivora, in all of which the foramen, besides its other 

 differences of position, is quite below the zygomatic ridge in question. 



The interorbital part of the upper surface of the cranium (Plate XIII. fig. 1, n) is 

 remarkable in the marsupial Carnivora for its great breadth, especially as compared with 

 that of the cerebral portion of the cranium ; the transverse diameter of this part at the 

 middle and highest part of the upper border of the squamosals is, in the Dasyurus 

 ursinus, less than half the same diameter of the narrowest part of the interorbital portion 

 of the cranium. In the Tiger, Lion, and Felis spelcca the diameter of the interorbital 

 space is one-seventh less than that of the cranium of the Thylacoleo, taken across the 

 same part as in the Dasyurus. In the Thylacoleo the least diameter of the interorbital 

 surface is 2 inches 10 lines ; the diameter of the cranium opposite the middle of the 

 upper border of the squamosals, 2-', is 1 inch 3 lines. 



The broad interorbital platform of the Thylacoleo, with a broad and shallow depression, 

 and two slight lateral convexities at its anterior half, passing posteriorly into an almost 

 flattened surface, decreasing to the point where the temporal ridges {t') meet above the 



