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



stretched from the root and adjacent part of the processus gracilis to the neck and head> 

 but a narrow strip of lamellar hone running with that process far in front of the head 

 into the Glaserian fissure. Indeed the thin sickle-shaped processus gracilis of Equus 

 is probably a modification of it. The Rhinoceros's malleus approaches a type very 

 frequent in the Insectivora, the Bats, the Marsupials, and some Edentata, as Priodon, 

 where the processus gracilis is elongated in a very similar manner. But more will be 

 said on the subject when the ossicles of the latter groups are discussed. 



The incus of Rhinoceros is of a very peculiar form, the body being very broad and 

 shallow, and the crura both widely divergent ; the posterior is long, stout, and blunt- 

 pointed; the processus longus is rather short, boldly curved, deeply grooved on its inner 

 aspect, and bears on its extremity a greatly developed Sylvian apophysis, pedunculated 

 with a slightly concave oval surface towards the stapes. It is absolutely and, as I 

 believe, proportionally the largest Sylvian apophysis existing, greater than the same in 

 Galeopithecus, to which Hyrtl gives the palm ; but he does not describe the ossicula of 

 the Rhinoceros. 



The stapes has a very large head, slightly convex, to fit the apophysis ; the posterior 

 cms is quite straight, the anterior curved forward just before its insertion. In the spe- 

 cimen in the College collection there is a thin lamina of bone between the upper halves 

 of the crura. The base is broad and convex. 



The ossicula of R. sondaicus and R. sumatrensis are almost identical in character. 



Among the Tapiridjji, the malleus of Tapirus bairdi (PL LXI. fig. 2) resembles con- 

 siderably that of the Rhinoceros, particularly in the large excavation for the incus, and 

 the very slight development of the upper part of the head ; but the neck is shorter, more 

 curved, and not so closely defined in front from the lamina ; the manubrium is not so 

 much bent inwards, and is very little curved outwards at the tip, which is less broadly 

 spatulate. Besides the processus muscularis there is a small tubercle on the inner side of. 

 the neck, not on the root of the manubrium as in Rhinoceros. The lamina is broad, and 

 runs into a similar processus gracilis, which is slender and fragile. 



The incus has a very broad body ; its interior segment is much less developed than the 

 posterior, by which it differs from Rhinoceros and approaches Equus. 



In the Equid^e, the typical Equus caballus (PI. LXI. fig. 3) has a malleus with a well' 

 developed globular head, exceeding, in that respect, other Ungulates, and a wide, deeply 

 cut articular surface, whose edges are raised above the level of the rest of the head, upon 

 which it encroaches very little. The facets are almost plane, but slightly saddle-shaped ; 

 the groove between them is not well marked. The neck is rather long, somewhat 

 flattened, and twisted a little outwards near the root of the manubrium, which leaves 

 it at a right angle, is long, but broader at the base than in the Tapir and Rhinoceros. 

 The manubrium is only slightly spatulate and recurved at the tip, and has a narrow but 

 well-bordered outer surface. The processus brevis is represented by a blunt tubercle, 

 much bent forwards ; the muscular process is a small tubercle on the inner side of the 

 neck, close to the root of the manubrium. The processus gracilis is long and sickle- 

 shaped, not nearly so broad as in Rhinoceros ; and there is little trace of a lamina : 

 hence the equine malleus is a less specialized bone than that of the other odd-toed 



