OF THE MARSUPIALIA. 393 
margin of a vertical plate of bone, a more or less flattened surface extended between the 
external ridge and the internal process, or inflected angle. 
In the Oposswms this internal angular process is triangular and trihedral, directed 
inwards, with the point slightly curved upwards. In the Dasyures it has a similar form, 
but the apew is extended into an obtuse process. In the Thylacine the base of the in- 
flected angle is proportionally more extended ; and a similar structure is presented by 
the jaw of the fossil Phascolothere. In the Perameles the angle of the jaw forms a still 
longer process ; it is of a flattened form, extended obliquely inwards and backwards, and 
slightly curved upwards. In the Potoroos and Phalangers the process is broad, with 
the apex slightly developed ;—it is bent inwards, and bounds the lower part of a wide 
and deep depression on the inside of the ascending ramus. In the Great Kangaroo the 
internal margin of this process is curved upwards, so as to augment the depth of the 
internal depression above mentioned. The internal angular process arrives at its 
maximum of development in the Wombat", so that the breadth of the base of the ascend- 
ing ramus very nearly equals the height of the same. This broad base also inclines 
downwards and outwards from the inflected angle, and the same peculiarity occurs in 
the jaw of the fossil Phascolothere. 
{In the Koala* the size of the process in question is also considerable, but it is com- 
pressed and directed backwards, with the obtuse apex only bending inwards ; so that 
the characteristic flattening of the base of the ascending ramus is least marked in this 
species. There is no depression on the inner side of the ramus in the Koala, but the 
smooth surface is simply pierced near its middle by the dental artery. There is a cor- 
responding perforation on the external surface of the ascending ramus, upon which we 
observe the external muscular depression bounded below by a broad angular ridge. In 
the Dasyure there is no external perforation corresponding with the dental canal on the 
‘inside of the ramus. The ramus is likewise entire in the Petaurists, Phalangers, Pera- 
meles and Opossums. In the Wombat the ascending ramus is directly perforated by a 
round aperture* immediately posterior to the commencement of the dental canal: the 
corresponding aperture is of larger size in the Kangaroo ; but in the Potoroos both the 
external and internal depressions of the ascending ramus lead to wide canals, or con- 
tinuations of the depressions, which pass forwards in the substance of the horizontal 
ramus, and soon uniting into one passage, leave a vacant space in the intervening bony 
septum. This structure, if it had only existed in the jaw of a fossil Marsupial, would 
have supported an argument for its saurian nature, on account of a nearly allied struc- 
ture in the jaw of the Crocodile. The posterior aperture of the dental canal is situated 
in the Potoroos and Wombat, as in the Stonesfield fossils, just behind the last molar 
tooth ; and in the Wombat a vascular groove is continued from the foramen, along the 
1 Pl. LXXI. fig. 6 d. ® Pl. LXIX. fig. 4. 
* A bristle is represented as passing through this aperture on the left side of the lower jaw, in Pl. LXXI. 
fig. 6 d. 
3F2 
