OF THE MAMMALIAN OSSICULA AUDITUS. 419 



Dasyprocta, and Hydrochcerus, but to an extreme degree in Aulacodus, Capromys, and 

 especially in Chinchilla. The stapes is small, with well-developed crura, not very diver- 

 gent. A bony canal runs between the crura in some specimens from several species, but 

 is not constant. 



V. In the Duplicidentati the characters of the ossicles are rather central. The malleus 

 is of much tbe same form as in the less-typical Muridse ; but the head is less developed. 

 There is never any fusion of the malleus and incus in Lepus. 



The Ossicula op the Ungulata. 

 The different families of Perissodactyla offer more sharply defined characters in their 

 auditory ossicles than do the even-toed Ungulates. 



Suborder Perissodactyla. 



Among the Rhinocerothxe, the ossicula are all very small in proportion to the 

 size of the animal. In Rhinoceros Mcomis (PI. LXI. fig. 1) the malleus, from the top 

 of the head to the top of its long manubrium, measures one centimetre, the incus is 

 two millimetres high between the crura, and its body is barely four millimetres broad, 

 all much inferior measurements to the same in a Horse, and hardly above the pro- 

 portions in a Tapir. 



The malleus has an extremely deep and "wide articular surface, reducing the head to a 

 mere cup-shaped process, with none of the free globular portion seen more or less in 

 most mammals. The upper facet (very prominent from the ill-development of the head) 

 is not as large as the lower ; both are slightly saddle-shaped, and run into each other at 

 the bottom of the deep excavation without any sharp dividing ridge. The neck is cylin- 

 drical, curved, and rather narrow, bordered anteriorly by the lamina. The manubrium 

 . is very long and slender : it is bent somewhat inwards as it leaves the neck, curving 

 boldly outwards near the extremity, which is distinctly spatulate. It forms nearly a 

 right angle near the neck ; a well-rounded tuberosity occupies the site of the processus 

 brevis ; there is a small tubercular processus muscularis on the inner aspect of its root. 

 The sides of the manubrium are flattened and narrow throughout, the inner border is 

 rounded, not sharp ; the outer angle is still bordered, though extremely narrow. In 

 front of the neck is a laminar expansion (PI. LXI. fig. 1, I), which is continued (rather 

 than merely blended below, as in Carnivora and Ruminants) into a very large lamelliform 

 processus gracilis (p g), shaped like a streamer or pennant, and measuring, in a speci- 

 men in the College, twelve millimetres, the manubrium being only nine millim etres long. 

 A process from the head (p h m) bounds the anterior and upper border of the 

 lamina. 



Comparing this bone with the corresponding ossicle in other Perissodactyla and 

 Artiodactyla, the presence of a lamina might lead the observer to the assumption that 

 the malleus of Rhinoceros is more like that of the Pigs and Ruminants than that of the 

 Equidse ; the same remark applies to the very similar malleus of Tapirus. But a very 

 little consideration must convince him that the lamina in the Rhinoceros is of a different 

 type from that of the even-toed Ungulates. It is not, as in them, a broad lamella of bone 



