OF THE MAMMALIAN OSSICULA AUDITUS. 389 



on the inner edge of the manubrium nearer the root than the tip. The outer aspect 

 of the manubrium facing the tympanic membrane, though very narrow, is distinctly 

 bordered on from both sides by sharp edges, till it dilates very gradually into the narrow 

 spatulate, recurved extremity. This distinct outer surface to the manubrium is seen 

 in the Carnivora, Ungulata, and many Rodents. As it is in the E/odentia that the 

 processus muscularis is so frequently placed completely on the manubrium, the extensive 

 lamina being generally absent in that order, it follows that the malleus of Chiromys is 

 more allied to the Glires than to the flesh-eating and ungulate Mammalia. 



The incus is remarkable for the sharp projection backwards of its posterior segments ; 

 the crura are stout, short, but neither are strongly divergent ; the Sylvian apophysis 

 is extremely elliptical, or rather key-hole-shaped in outline, being broad horizontally 

 and very thin vertically. The crura of the stapes are stout, the posterior much bent, 

 as in Homo ; the intercrural space is wide, and not occupied by a bony canal in the 

 recent skull. 



The above researches into the ossicula of the Platyrrhini and the Lemuridae will now 

 be briefly summarized. 



I. In Ateles the malleus is of peculiar shape. It has a short neck and a rounded 

 prominence corresponding to the processus brevis. The articular surface is shallow, as 

 in all the Cebidse. The incus has not a very high body ; the crura of the stapes are 

 longer than in other monkeys. 



II. In Mycetes and Pithecia the neck of the malleus is quite suppressed (together 

 with the processus brevis), and the manubrium at its root runs in the long axis of the 

 head. The incus has a very high narrow body. The stapes, in these and the genera of 

 the Cebida? yet to be mentioned, has not so long crura as in Ateles, but is of the 

 same form as in the Old-world monkeys. 



III. In Cebus, Nyciipithecus, and Saimaris the malleus much resembles that of 

 Mycetes ; but the head is bent on the root of the manubrium. In Cebus the body of 

 the incus is not higher than in Ateles ; but in the other genera it is almost as high as in 

 Mycetes or Pithecia. 



IV. In the Hapalidae the malleus has a rather deeper articular surface than in the 

 Cebidse ; it is quite neckless ; and the head is bent on the manubrium. The incus is 

 generally high in the body. In the Marmoset the crura of the stapes are often fused for 

 some distance below the head, as in mammals of a very low grade. 



V. Among the Lemuridae, the Nycticebidse, Galaginidse, and Propithecus (at least in 

 young specimens of P. diadema) much resemble the Hapalidae and Cebus in the malleus ; 

 but the articular surface is deep, deeper than even in Hapale ; the head is very 

 short, and strongly bent on the manubrium. The incus has a very high body in the 

 Galagos, but not in the Nycticebidse. Tarsius and Perodicticus resemble Nycticebus. 



VI. But in Lemur the malleus loses the specialized form common in the other 

 Lemuridse and the New-world monkeys. There is a constricted neck, and a more or less 

 developed processus brevis ; the manubrium forms a distinct angle with the neck, 

 instead of the head being bent on it as in the Galagos &c. The incus is not high and 



SECOND SEMES. — ZOOLOGY, VOL. I. 3 G 



