478 MR. A. H. G. DORAN ON THE MORPHOLOGY 



many Cetaceans and Seals are in no way homologous with that of this section, for a reason 

 given in the last paragraph. This group will include the remaining families of the 

 Didelphia — to wit, the Peramelidse, Phalangistidse, Dasyuridse, and Phascolomyidse. 

 Among the larger species in these groups a small aperture occasionally exists. 



The malleus of an adult Kangaroo (Macropus major, PI. LXIV. fig. 31) is of light con- 

 struction, though in no wise so thin and papery as in the Bandicoots. The head is small, 

 and only moderately developed, as in the majority of laminated mallei in the Monodelphia ; 

 though much flattened laterally, it is not "broad in that sense, nor does it project in any 

 direction beyond the articular surface. This latter is placed more superiorly than behind, 

 as in most Edentates, owing to the position of the incus. It has a raised and prominent 

 border; owing to the lateral flattening of the head, it is rather narrow, but deeply cut. 

 Its facets are of the character seen in most of the higher Mammalia, and hence differ 

 from the type of Man, Monkeys, and Manis. The upper or, rather, the anterior is wide 

 and almost flat ; it is twisted a little more inwards than the lower, which is narrow and 

 convex; the groove hetween them is well marked. The neck is rather short and slightly 

 curved ; the lamina is very narrow. The long and slender manubrium forms a right 

 angle (or even a few degrees less than 90°) with the neck ; the site of the processus hrevis 

 is very obtuse ; and the sides are compressed, though not broad even near the root ; there 

 is a distinctly bordered outer surface, as in Carnivora, Ruminants, and others, very 

 narrow, and hut slightly spatulate near the tip, which is hardly perceptibly recurved. A 

 very slight trace of a tubercle at the junction of the neck with the root of the manubrium 

 represents the processus muscularis. 



Prom the front projects the remarkable processus gracilis, already well known to ana- 

 tomists *. It is much longer than the manubrium, and curved downwards and back- 

 wards, and also somewhat outwards. It is attached by membrane (or, in some individuals, 

 actually ankylosed) to the tympanic ring, and is flattened and papery in character, rather 

 broader below than at the root, but ending in a point ; near the body of the malleus it is 

 separated from the lamina by a thin ridge ; and the narrow lamina itself is prolonged on 

 the anterior edge of the processus gracilis. The anterior part of the head of the bone is 

 not prolonged on to the front of the lamina, as in most laminated mallei ; on the con- 

 trary, it is separated from the lamina by its very high border f . 



Such is the malleus of Macropus. Let us review its peculiarities, and compare them 

 with those of the same ossicle in higher mammals ; for the more the latter possess cha- 

 racters in which the Macropodian malleus differs from that of the Primates, the lower, 

 in that respect, must such Monodelphia be considered. 



In the lateral flattening and general form of the head the mallei of Carnivora and 

 PLuminants, and other Monodelphia where the lamina is well developed, all resemble the 

 malleus of Macropus ; so does that of Myrmecophaga and Tamandua ; only in the Ant- 



* See Hyrtl, op. cit. ; Peters, 'Berichte der Berliner Academie,' 1867; his conclusions in his paper for that year on 

 this subject were admitted to be incorrect by himself in an article in the same publication, 1868. See also, on the 

 latter, Huxley, Proc. Zool. Soc. 1869. 



t This high border is most marked on the external aspect of the malleus. It is very distinct in all the Kangaroos 

 and Wombats. (See PI. LXIV. fig. 31.) 



