Miscellaneous. 389 



even in the Marsupialia. The absence of the articulation with the 

 lower jaw seemed to me to be of the less importance, as the qua- 

 drate bone is also inconstant in its other unions, and only that with 

 the squamous portion of the temporal is constant. That a distinct 

 bone, which is constant throughout the whole series of the Mam- 

 malia, should at once disappear, seemed to me to be improbable ; 

 nor could I accept the small fragments of bone found in birds, by- 

 some observers, as representing it. 



I could never reconcile myself to the opinion, supported especially 

 by Reichert and Huxley, that the incus of the Mammalia is the 

 homologue of the quadrate bone, both on account of the objections 

 raised against it by J. Miiller*, who had the opportunity of care- 

 fully examining the preparations made by M. Eeichert for the 

 proof of his opinion, and also because it seemed to me very impro- 

 bable that the incus, which in the OrnithorhyncJius does not occur at 

 all, or only appears as a minute rudiment, should suddenly make 

 its appearance again in the Birds in such gigantic proportions and 

 in a totally different position, not to mention the difficulty of inter- 

 preting the incus and malleus which certainly likewise occur in a 

 cartilaginous rudimentary state in Birdsf. 



Leaving this last circumstance, especially, out of consideration, 

 from the similarity which two parts issuing from or connected with 

 Meckel's process (namely, the articular portion of the lower jaw in 

 Birds and Amphibia, and the malleus of the Mammaha lying behind 

 the lower jaw) present to one another at a certain period of deve- 

 lopment, a conclusion is arrived at as to the homology of these 

 parts, upon which a number of other hypotheses upon the homologies 

 of other parts of the skeleton (e. g. in the fishes) are supported ; and 

 the latter, of course, fall if the former be erroneous. 



At the present moment, when I am occupied with the conclusion 

 of other investigations, I should hardly have been led to take up 

 again a question which has been so long in dispute, if Mr. Huxley, 

 who had already % given his decided adhesion to the opinion of the 

 homology of the quadrate bone and the incus, had not, in a memoir 

 upon the classification of Birds, otherwise containing much that is 

 admirable, and which is destined to find a very large circle of 

 readers, represented the matter as if all doubt upon the point in 

 question had been got rid of §. 



As it appeared to me that a solution of the question was most 

 likely to be found among the lower MammaHa, which approach 

 Birds in so many respects, I first sought for it among the Monotre- 

 mata, but have been compelled to interrupt this investigation for 

 the present, and in the next place took young Marsupials in hand. 



* Archiv fiir Anatomie und Physiologic, 1838, p. clxxxvii. 



t Even if there may be some doubt with regard to the incus in Birds, 

 this must be quite baseless with respect to the malleus. But the bone 

 which is denominated incus in the Mammalia is always situated between 

 the stapes and the malleus. 



X Lectures on the Elements of Comparative Anatomy. London, 1864, 

 pp. 229 et seq. 



§ Proc. Zool. Soc. London, 1867, p. 416. 



