76 



PEOFESSOR OWEN ON THE FOSSIL MAMMALS OF ATJSTEALIA. 



this significant part of the skull being preserved in the present fossil as is formed by 

 the zygomatic process of the squamosal demonstrates the wide difference from the semi- 

 cylindrical transverse canal characteristic of the ginglymoid joint of the lower jaw in 

 placental Carnivora. The surface, though of great transverse extent, was probably 

 carried out further in that direction by the malar bone (to judge by the analogy of 

 the Basyurus, Philosophical Transactions, 1859, Plate XIV. fig. 2) ; but this part of 

 the zygoma has been broken away. There is a striking similarity, indeed, in the kind 

 of mutilation which the fossil skull from the freshwater deposits at Colungoolac {ib. 

 p. 310), and that from the same formations channelled by the Condamine, has undergone. 

 The occipital condyles, zygomatic arches, and postorbital processes have sufiored, dif- 

 fering only in the degree in which these projecting parts have been broken away during 

 the apparently similar cosmical violences to which both fossils have been subject. Besides 

 the post-glenoid ridge (Plates IT. & III. I) in Thylacoleo, there is a narrower boundary 

 wall descending in the inner or mesial end of the articular surface, nearly as low as the 

 posterior one ; it renders the surface concave in the transverse direction ; and against 

 this " entoglenoid process" (ib. e) abuts the apex of a thick obtuse triangular mass of 

 bone, with the base turned toward the descending basisphenoid ridge, but separated 

 from it and from the end of the pterygoid by a groove. This convex portion of bone 

 (Plate III. e) appears to be developed from the base of the alisphenoid, and to have con- 

 tributed to the tympanic cavity, like the second "bulla ossea" in Perameles* ; it was 

 broken away on both sides in the first-described skull, but the pneumatic cavity by 

 which it was excavated is partly shown on the left side (Philosophical Transactions, 1859, 

 Plate XIV. e) ; its base is perforated by the " foramen ovale." 



In the present skull the cranium has been broken across lengthwise, and almost 

 horizontally, exposing the extension of the air-sinuses (Plate IV. fig. 4) from the nose 

 to the occiput, raising the outer table of the cranium nearly 2 inches above the 

 inner one at the middle of the intertemporal ridge, and showing the small cerebral 

 cavity restricted to the lower and hinder half of the cranium. The length of this cavity 

 is 4 inches, its breadth 3 inches, its height 2 inches. Neither falx nor tentorium was 

 ossified. The anterior boundary of the "sella" is indicated by a transverse rising pro- 

 duced into a pair of small retroverted " clinoid" processes, but there is no depression 

 below the level of the cranial surface of the basisphenoid. The rhinencephalic com- 

 partment is relatively large. 



In all the characters of the cranium shown and described in the original specimen the 

 present fossil corresponds therewith. The posterior palatine vacuity, indicated by the 

 smootlily convex inner border of the roof of the mouth parallel with the hind half of 

 the sectorial tooth (in Plate XIV. fig. 1, d, torn, cit.), is shown in the present skull 

 (Plate III. d) to be the fore part of the wide and advanced " palato-nares ; " they are 

 divided, mesially, by the presphenoid rostrum and vomer, and arc bounded, laterally, 

 by an extension of the ])alatal process of the maxillary and of the palatine to the ptery- 

 * Cyclopaedia of Analoniy and Physiology, vol. iii. Art. Marsupialia, fig. 90. 



