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



in the suppression or peculiar development of any of their processes, which are so remark- 

 able in the Cetacea. 



III. Not only do they differ clearly from the Cetacean ossicula, hut their modified 

 general structure may he said to mask or obliterate any homologies to the ossicula in other 

 mammals, which otherwise might be observable — the only exception being the approach 

 to a quadrilateral type of stapes in Kalicore, apparently more marked in Ualitherium, 

 which, whatever be its value, cannot fail to remind the anatomist of the bovine form of 

 that ossicle. 



IV. Halicore differs distinctly from Manatus in the antero-posterior shortness of the 

 body of its malleus, in the smallness of its articular facets, in the form of its manubrium, 

 in the tubercle on the outer and posterior aspect of the body of the incus supporting the 

 articular surface, and in the shorter incus with more divergent crura. 



V. In Hhytina the malleus and incus appear very like those of Manatus. But in 

 Ualitherium the characters of the ossicula are extremely intermediate — the incus being 

 most like that of Manatus, the stapes like the Dugong's, and the malleus possessing 

 features seen in both. 



VI. The distinguishing feature by which ill. americanus may be known, by its ossi- 

 cula, from M. senegalensis, is a slight difference in the characters of the malleo-incudal 

 articulation. 



The Ossicula of the Edentata. 



As is the case with the rest of the skeleton, the ear-bones in this Order exhibit con- 

 siderable variety of type ; the characters of the malleus and incus are very general ; 

 whilst the stapes assumes the Sauropsidan form in one group, and approaches it in 

 several others. 



In the two recent genera of the Phytophaga the malleus offers points of difference too 

 marked to be overlooked. This ossicle in the Ai, or Three-toed Sloth (Bradypus tridae- 

 tylus, PI. LXIV. fig. 1) has a rounded, well-developed head, projecting a little upwards, but 

 more forwards, and rather flattened laterally. The articular surface is deeply cut, the facets 

 lying almost at right angles to one another ; they are narrow horizontally ; the upper is 

 almost plane, the lower perceptibly convex ; the neck is long, slender, and almost straight. 

 By laying the malleus of Homo by the side of one from this Edentate, the identity of the 

 sigmoid ridge of the former with the much less curved neck, just described, in the latter 

 will at once become very evident. The processus gracilis forms a very acute angle with 

 the neck, leaving a narrow space between them, homologous with the lamina, but filled 

 up with thick and friable rather than lamellar bone. There is no trace of any processus 

 muscularis, either on the neck or the handle. The manubrium forms an angle of over 

 150° with the rest of the malleus ; it is of medium length, very thin, and compressed 

 laterally, and broad at the base, where, externally, is seen a sharp angle, representing the 

 processus brevis. The external aspect is bordered from the sides by sharp edges, as in 

 the Carnivora, &c. s but very narrow ; the extremity is slightly spatulate, and perceptibly 

 recurved. 



