OF THE MAMMALIAN OSSICULA AUDITUS. 421 



Ungulates, and far more removed from the Artiodactyle form. The incus is very much 

 larger than that of the Rhinoceros, both absolutely and proportionally. Its body is rather 

 broad, and cannot be distinguished posteriorly from the stout, short, and little-divergent 

 processus brevis ; the anterior part is very little developed ; the processus longus is more 

 slender than the processus brevis, though still rather broad at the base ; unlike the pos- 

 terior crus, it diverges considerably from the body. The stapes is quite triangular, has 

 a well-developed head, with extremely straight crura, not very divergent towards the 

 base, and inserted a perceptible distance from each extremity. The base itself is broad 

 and almost plane. 



In Equus asinus, and still more in E. zebra, the processus muscularis of the malleus 

 is more developed than in E. caballus, appearing as a slightly curved blunt-pointed pro- 

 cess. The incus in both the former has a slender and more divergent processus brevis ; 

 in the Zebra the whole body is more developed. The Sylvian apophysis is a fiat sessile 

 disk ; in adults it fuses more or less completely with the processus longus, as in Man. 

 The stapes of E. zebra is very horse-like, the head being very broad and stout, the crura 

 straight, and the aperture triangular, with sharp angles; the base is thick, with an 

 umbo towards the vestibule. The stapes in E. asinus has a smaller head ; the anterior 

 crus is distinctly curved ; and the intercrural aperture is round rather than triangular. 

 A tubercle, with an ossified piece of the stapedius tendon attached, is often seen in 

 the stapedes of the Equidse and also in many Artiodactyles. 



Subfamily Artiodactyla. 



This group is interesting for the frequent recurrence of the broadly laminate form of 

 malleus which prevails among the fissipede Carnivora. The incus, as will be shown, is a 

 bone of great interest and distinctive value in these animals. 



In the Hippopotamus (PI. LXI. figs. 4 & 5) the malleus has a large head, with a well- 

 developed spherical upper aspect, and a very broad articular surface, of which the upper 

 facet is of great breadth, almost plane, but has a vertical convex ridge near the outer 

 border ; while the lower facet is very narrow, and vertically much elongated, so as to be 

 tongue-shaped and quite convex in both directions. They blend together undivided by 

 any sharp groove ; and the entire surface is somewhat shallow. The neck is short, very 

 broad towards the neck, and constricted close to the manubrium ; it is considerably 

 flattened laterally ; and from its inner aspect, a considerable distance from the root of 

 the handle, springs a long, straight processus muscularis, of equal thickness throughout, 

 and hence blunt-pointed. The manubrium is long, it leaves the neck at an obtuse angle, 

 and is flattened laterally, but not very broad at the base. The processus brevis is a 

 sharp angular projection bent rather backwards ; the outer aspect of the handle is sharply 

 bordered from the sides, and spatulate at its extremity, which is but a little recurved ; 

 the whole process is almost straight. The processus gracilis is very slender and united 

 for some distance to the neck and head by spongy, not lamellar bone. 



This bone is very like the same in the pig, the chief distinction being in the cha- 

 racter of the articular surface ; the spongy bone between the neck and processus 



SECOND SERIES. — ZOOLOGY, VOL. I. 3 L 



