OF THE MAMMALIAN OSSICULA AUDITUS. 487 



IV. That in the same respect the American Opossums or Didelphyid.se must he con- 

 sidered the highest of the Marsupials. The malleus is, in type and consistence, similar 

 to that of many Insectivora ; the incus has the hody and short crus as well as the pro- 

 cessus longus well developed ; and the stapes is more perfectly bicrurate than in any other 

 allied family. 



V. The Macropodidge are very central among Marsupials in their ossicula. The 

 malleus is of low type, hut tolerably firm osseous consistence ; it bears the peculiar 

 highly-developed foliaceous processus gracilis also seen in the "Wombats ; the incus is 

 fairly developed ; and the stapes is always partially bicrurate. 



VI. The Phalangistidse come next in order. They are decidedly inferior to the 

 Kangaroos in that the stapes is generally (though not invariably) columelliform ; more- 

 over the malleus is of the form seen in a new-born Macropus; but in the size and 

 good development of all parts of the incus they are as high or even higher than the 

 American Opossums. Phascolarctos is lower in all respects than JPhalcmgista ; its 

 malleus is of a very distinctive character. 



VII. The Wombats are slightly lower than the last family, the stapes being always 

 columelliform, and the incus having a rather short processus brevis, but a stapedial 

 crus rather of the Perameles type. The malleus is not so much of high type as an 

 extreme form of the specialized corresponding ossicle in Macropus, the processus gracilis 

 being very large, curved, and flattened. 



VIII. The Dasyures have the stapes invariably columelliform, and the incus of low 

 type; but all their ossicles are of more solid consistence than in the Bandicoots 

 (Peramelidse). 



The Ossicula op the Monotremata. 



Next to the ear-bone of Man, those of Echidna and Omithorhynchus are of all other 

 mammalian ossicula the best known to the anatomist. From the conformation of the 

 base of the skull in the Monotremata, the malleus cannot fail to obtrude itself on the 

 glance of the student cursorily examining the cranium. Then these little bones are of 

 profound interest to the morphologist when studying this subclass, which is so un- 

 doubtedly allied in many respects to the Sauropsida, where two out of three ossicula 

 are suppressed. Good general descriptions of the ear-bones of the Monotremata, with 

 clear figures, are to be found in the works of Huxley *, Hyrtl t, Peters %, and others. 



I leave such important questions as What bones are the homologues of the mam- 

 malian malleus and incus in the Sauropsida ? to distinguished authorities in the united 

 branches of morphology and embryology. Next, I need hardly remind the anatomist 

 that, as far as the ossicles are concerned, the Monotremata wear a perfectly mammalian 

 uniform, having malleus, incus, and stapes. If any theorist consider this Order more 

 Sauropsidan than mammalian, on account of the most marked feature in the first two 



* Proc. Zool. Soo. 1869 ; see woodcut, p. 404. t Op. cit. 



X " Ueber das os tympanicum und die Grehbrknochelchen der Schnabelthiere &e." Monatsberichte der Akad. der 

 Wisscnsch. Berlin, 1867. 



3t 2 



