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



nated form of BZomo and the broadly laminated type of the Carnivora and Artiodactyla*. 

 The manubrium of Cholcepus is longer than in Bradypus, and forms little more than a 

 right angle with the neck ; this alone gives the whole malleus a different aspect from 

 that of the Ai. The processus muscularis is represented by a distinct tubercle on the 

 inner side of the root of the manubrium ; the latter is even broader than in Bradypus. 



The incus of Choloepus does not differ from that of the A'i ; the Sylvian apophysis is 

 of the same character. 



The stapes of the Unau has even less divergent crura than that of Bradypus; the 

 aperture is either very small or quite obliterated : these two conditions may be seen in 

 different examples in the College collection. 



Turning to the Entomophaga, the ossicula in the genus Basypus are larger than in 

 the Sloths. In the College collection all three in Basypus villosus are absolutely 

 larger than in Bradypus. 



In the fine malleus of the 6-banded Armadillo {Basypus sexcinctus, PL LXIV. fig. 4) 

 the head is well formed and globular, without being produced forward or in any par- 

 ticular direction. The articular surface is deeply cut, the facets lying at right angles to 

 each other ; the upper is very wide and nearly plane, the lower is barely half its area 

 and more convex. The neck is short and bent ; the processus gracilis is arched towards 

 the body of the ossicle, and then curved downwards and forwards; the space thus formed 

 is narrow, and occupied by a true lamina of really lamellar bone. The processus mus- 

 cularis is a bony tubercle on the inner side of the neck, close to the root of the handle. 



The manubrium is long and straight ; it forms an angle of about 140° with the neck ; 

 it is compressed laterally, but not very broad at the base. A true processus brevis 

 exists — the angular projection at the external aspect of the base being considerably 

 everted, and hence is not merely the simple apex of an angle formed by the upper edge 

 of the base and the outer side of the manubrium. This outer aspect, as in Bradypus, is 

 very narrow, yet distinctly bordered from the sides ; the extremity is very slightly 

 spatulate and but little recurved. In the well-formed head, decurved processus gracilis, 

 narrow lamina, and long manubrium this malleus recalls that of the Horse (Bquus). 



The body of the incus (PI. LXIV. fig. 4) is shallow and broad ; the processus brevis 

 (which lies much more superiorly than posteriorly) is short and sharp-pointed, it 

 diverges very little. The processus longus is thin, long, and very divergent ; the pro- 

 cessus Sylvii is absolutely sessile, and hardly separated in the adult by any trace of a 

 groove ; but a distinct channel is to be seen in incudes from new-born Armadillos. The 

 characters of the crura very plainly and completely divide Basypus from the Sloths. 



The stapes is a large bone of very light and elegant form (fig. 4). The head is long 

 and flattened, with a small tubercle for the insertion of the stapedius. The crura are 

 long, straight, and conspicuously slender ; they are well grooved towards the aperture, 

 which is very wide. The base is broad horizontally, but not very deep vertically ; it is 

 distinctly convex towards the vestibule. 



* Refer to the remarks on the human malleus (anted), particularly the description of the sigmoid ridge and its 

 homologies. 



