126 



Marsupialia. In all the species, the Petaurists excepted, the malar 

 bone forms the outer part of the articular surface for the lower jaw ; 

 and in the Dasyurus Maugei, Dasyurus Ursinus, Perameles, Hypsi- 

 prymnus and Macropus, the sphenoid ala forms the inner boundary 

 of the same surface ; but it does not extend so far backwards in the 

 Wombat or Koala. 



" The sphenoid bone has the same general form and relative po- 

 sition as in the ordinary IMammalia, but presents a similarity to that 

 in the Ovipara, in the persistence of the pterygoid processes as sepa- 

 rate bones. It is only in the Koala that I have observed a complete 

 obliteration of the suture joining the basilar element of the sphe- 

 noid with that of the occipital bone. 



" The chief peculiarity in the sphenoid bone is the dilatation of 

 the root of the great ala already alluded to ; this dilatation commu- 

 nicates with and is filled with air from the tympanum ; it forms the 

 hemispherical bulla ossea on each side of the basis cranii in the Da- 

 syures and Phascogales, and the large semiovate bullae in the Myr- 

 mecobius : but in the Koala the bull(E are still more developed, and 

 are produced downwards to an extent equal with the ex-occipital 

 processes ; they are somewhat compressed laterally, and instead of 

 the smooth and polished surface which characterize them in the pre- 

 ceding genera, terminate here in a rough ridge. The dilated air-cham- 

 bers or hullce of the sphenoid are relatively smaller in the Phalangers 

 and Potoroos than in the Dasyures ; and they are incomplete poste- 

 riorly in the Kangaroo and Wombat. In the Brush Kangaroo the 

 above process from the sphenoid joins the base of the large descend- 

 ing process of the ex-occipital. The pterygoid processes are relatively 

 largest in the Kangaroo, Wombat, and Koala, and present in each 

 of these species distinct hamular processes. In the Potoroo, Kanga- 

 roo, and Wombat, tlie sphenoid ala combines M'ith the pterygoid 

 process to form a large and deep depression opening externally. In 

 the Kangaroo, Dasyures, Koala and Wombat, the great alee of the 

 sphenoid articulate with the parietal bones ; but, by a veiy small 

 portion in the two latter species ; in the Perameles and Potoroos, 

 the sphenoid ala do not reach the parietals. 



" There is little to notice in the parietal bones except the oblite- 

 ration of the sagittal suture in those species in which a bony crista 

 is developed in the corresponding place : they present a singularly 

 flattened form in the Wombat, in an aged skull of which, and in a 

 similar one in the Kangaroo, I observe a like obliteration of the sa- 

 gittal suture. In the Kangaroo, Potoroo, Petaurus, Phalanger, and 

 Myrmecobius, there is a triangular inter- parietal bone. The cor- 

 responding bone I find in three pieces in the skull of a Wombat. 



" The coronal suture presents in most of the Marsupials an irre- 

 gular angular course, forming a notch in the frontals on each side, 

 which receives a corresponding triangular process of the parietal bone : 

 this form of the suture is least pronounced in the Myrmecobius and 

 Acrobates. A process corresponding to the posterior frontal augments 

 the bony boundary of the orbit in the Thylacine, the Ursine Dasyure, 

 and in a slighter degree in the Virginian Opossum. It is relatively 



