338 ANATOMY OF VERTEBRATES. 



Macropus, and Hi/psiprymniis murinus, the length of the skull 

 anterior to the orbit is equal to the remaining posterior part ; but 

 in a species from Van Dieman's Land {^Hypsiprymiius myosurus, 

 Ogiib.), the facial part of the skull anterior to the orbit exceeds 

 that of the remainder, and the arboreal Hypsiprymni from New 

 Guinea present a still greater length of muzzle. In most Mar- 

 supials the skull gradually converges toward the anterior ex- 

 tremity ; the convergence is more sudden in the Petaurists, 

 especially Pet. Bennettii\ but in the Perarneles lagotis the skull 

 is remarkable for the sudden narrowing of the face anterior to 

 the orbits, and the prolongation of the attenuated snout, pre- 

 serving the same diameter for upwards of an inch before it finally 

 tapers to the extremity of the nose. In- the Koala the corre- 

 sponding part of the skull is as remarkable for its shortness as 

 it is in the Per. lagotis for its length, but it is bounded laterally 

 by parallel lines through its whole extent. In nearly all the 

 Marsupials two long parapophyses project do"svnward from the 

 inferior angles of the occipital region. These processes are 

 longest in the Kangaroos and Koala ; in the Wombat they 

 coexist with the true mastoids, which are of larger size, fig. 

 220, 8. In the Opossums and Dasyures the paroccipitals are 

 short and obtuse ; in Acrohates they cease to exist, but they are 

 present in the larger Petaurists. 



The elements of the occipital neural arch remain longer dis- 

 tinct in IMarsupials than in most other Mammals. In the skull 

 of a half-grown Thylacine the basioccipital has coalesced mth 

 the exoccipitals, which almost meet above the foramen magnum. 

 The lateral sinus impresses the fore part of each exoccipital, and 

 then sinks into a canal which communicates or opens into the 

 precondyloid canal : from this another canal extends forward 

 through the side of the basioccipital. The superoccipital has 

 coalesced with the parietals and interparietal. The basisj)henoid 

 has coalesced mth the alisphenoids and the presphenoid, but 

 not with the pterygoids : it has no ' sella ' nor clinoid processes : 

 it is perforated by the entocarotid at its back and outer angle : 

 the canals converge forward and slightly upward, and terminate 

 above the middle of the basisphenoid. The alisphenoids have 

 the foramen ovale near their posterior borders : the foramen 

 rotundum is a longer canal. The posterior angles of the ali- 

 sphenoid expand into tympanic bullae: pterapophyses are sent 

 oif in advance which join both pterygoids and palatines. The 

 parietals have coalesced with each other, with the frontal, mth 

 the interparietal, and the superoccipital. The orbitosphenoids 



