OF THE MARSUPIALIA. 385 
presents in the marsupial, as in the placental Mammalia, various forms, each manifest- 
ing a physiological relation to the structure of the teeth, and adapted to the required 
movements of the jaws in the various genera. In the herbivorous Kangaroo the glenoid 
cavity forms a broad and slightly convex surface, as in the Ruminants, affording freedom 
of rotation to the lower jaw in every direction. In the Phalangers and Potoroos the 
articular surface is quite plain. In the Perameles it is slightly convex from side to 
side, and concave from behind forwards. In the Wombat it is formed by a narrow 
ridge, convex antero-posteriorly, considerably extended laterally, and slightly concave 
in the transverse direction’. This ridge is not bounded by any descending process pos- 
teriorly, so that the jaw is left free for the movements of protraction and retraction. 
But this structure is widely different from that which facilitates similar movements in 
the Rodentia: in these there is a longitudinal groove on each side, in which the condyle 
of the lower jaw plays backwards and forwards, but is impeded in its lateral movements ; 
these, on the contrary, are freely allowed to the Wombat, and the oblique disposition of 
the lines of enamel upon the molar teeth corresponds with the various movements of 
which the lower jaw of the Wombat is thus susceptible. In the Koala the glenoid cavity 
is a transversely oblong depression, with a slight convex rising at the bottom, indicating 
rotatory movements of the jaw: in the carnivorous Dasyures it forms a concavity still 
more elongated transversely, less deep than in the placental Carnivora, but adapted, as 
in them, to a ginglymoid motion of the lower jaw. The joint differs in the absence of 
an inter-articular cartilage in the marsupial Carnivores. In all the genera, save the 
Wombat, retraction of the lower jaw is opposed by a descending process of the tem- 
poral bone immediately anterior to the meatus auditorius and tympanic bone. The 
glenoid cavity presents a characteristic structure in most of the Marsupialia. In all the 
species, the Petawrists excepted, the malar bone forms the outer part of the articular 
surface for the lower jaw; and in the Dasyurus Maugei, Dasyurus Ursinus, Perameles, 
Hypsiprymnus 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 position as in the ordinary 
Mammalia, but presents a similarity to that in the Ovipara in the persistence of the 
pterygoid processes as separate bones*. It is only in the Koala that I have observed 
a complete obliteration of the suture joining its basilar element of the sphenoid 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 communicates with, and is filled with air from, 
the tympanum. It forms the hemispherical bulla ossea on each side of the basis cranii 
in the Dasyures and Phascogales, and the large semiovate bulla in the Myrmecobius ; but 
in the Koala the bulle are still more developed, and are produced downwards to an 
' Pl. LXXI, fig. 6. ® See the separate pterygoid of the Wombat, Pl. LXXI. fig. 6 c. 
3E2 
