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



In the Peramelid^ the malleus is of light and fragile construction, although wholly 

 osseous and not very different in character from the same ossicle in many older Mar- 

 supials (PI. LXIV. fig. 25). 



The head is very small, with a deeply cut articular surface, which has two facets, the 

 upper and anterior being the widest and plainest of the two, The neck is long and 

 thin ; it forms, by suddenly bending on itself midway between the head and manubrium, 

 a sharp projecting angle, as in the equally fragile malleus of the Soricidse. The slender 

 manubrium is rather broad and flattened at the base, and is blunt externally at the point 

 corresponding to the processus brevis. It ends in an almost styliform extremity. The 

 lamina is narrow, and joins the processus gracilis to form a curved process slightly broad 

 near the tip, as in the Dasyuridse ; this is fitted into the tympanic bone as in other 

 Marsupials. 



The incus of Perameles has a rather high and narrow body. The processus brevis is 

 rather long and thin, and not divergent from the body. The processtis longus is thin, 

 long, and very divergent ; it ends in a very conspicuous and perfectly elliptical Sylvian 

 apophysis, supported on a pedicle which is extremely thin at its attachment to the 

 stapedial cms, but becomes broad and flattened before it ends in the extremity of the 

 apophysis. This is but an extreme development of the condition so frequent in the 

 Didelphia. 



The stapes is completely columelliform ; and the column is as short as in the Passerine 

 birds ; the base, too, is rather wide vertically. This ossicle is generally imperfectly 

 ossified even in the adult Bandicoot. 



In Chceropus all the ossicula are of the type seen in Perameles (PI. LXIV. fig. 26). 



All the ear-bones of this family must be considered as of a very low type, the fragile 

 malleus of the adult recalling that ossicle in the foetus of higher mammals. The ill- 

 development of the processus brevis incudis and the persistent distinct character of the 

 Sylvian apophysis, as well as the perfectly columelliform stapes, combine to force upon 

 the observer the conclusion that, in respect of the ossicula, the Peramelidaa are the 

 lowest of the Didelphia; for in no other family are the little bones to be found all 

 three so thoroughly of low development in every detail. 



In concluding this review of the Ossicula of the Marsupialia, it may be said, by way of 

 a summary: — 



I. That the ear-bones in this subclass are always of a low type, yet not as a rule so 

 inferior to those of the Monodelphia as might be inferred, judging from the rest of 

 their skeletons. 



II. That no point showing a low grade of development in any ossicle in any Mar- 

 supial is not occasionally met with in higher mammals, excepting that in the latter the 

 ear-bones are never seen to retain to so high a degree the foetal consistence as may be 

 observed in the adult Terameles. 



III. That the Bandicoots or Peramelidse are, in respect of their ossicula, the lowest 

 family in the whole subclass, both in the type of all three bones, and in their frail 

 papery consistence compared with the rest of the cranium. 



