ORGAN OF HEARING. IN MAMMALIA. 233 



The conch is small and erect in the Wild-hogs, larger and 

 pendant in the domestic breeds. 



In the Anoplothcre the bony outer aperture of the ear was 

 round and horizontal, the passage directed from the tympanum 

 backward. The diameter of the semicircular canals, as in most 

 other Ungulates, is relatively less than in most small Lissence- 

 phalous Unguiculates. The lower ridge of the petrosal is less 

 marked in Camels than in true Ruminants. In these the stapes is 

 usually arched, widely open, with thickish crura, grooved inter- 

 nally, fig. 175, c, Bubalus, the base a long oval. In the Ox the 

 membrana tympani is oval ; the handle of the malleus extends 

 from above obliquely downward and forward to one-fourth of 

 the long diameter from the small end, and lies near the anterior 

 part of the circumference ; consequently the posterior fibres di- 

 verging from the handle are longest : in the stapideus muscle is 

 imbedded at the passage of the carneous into the tendinous part, 

 a roundish ossicle, about three-fourths of a line in long diameter, 

 and one-third of a line in short diameter. The tympanic bone is 

 compressed and produced into a long auditory canal with a 

 trenchant lower border, and the outlet almost horizontal. The 

 ear-conch in Ruminants is commonly characterised by three 

 vertical rows of hairs longer than the rest on the inner surface. 



The external ears of the Horse, fig. 156, are most expressive 

 appendages, in their extensive, rapid and various movements. 

 The tympanic bulla is divided by an unusually regular series of 

 radiating plates. The stapes, fig. 175, d, is an elongate triangle, 

 with crura of unequal thickness, a produced cervix, and narrow ob- 

 long base. Both the stapideus and tensor tympani have thick fleshy 

 portions : in the stapideus of the Horse there is an ossicle, smaller 

 than in the Ox, and of a longish shape, thicker in the middle. 

 The auditory chamber of the Tapir is small : the tympanic does 

 not dcvelope a meatus externus : the part supporting the mem- 

 brane early coalesces with the squamosal and the post-tympanic 

 part of the mastoid. The base of the stapes is elongate, fig. 

 179, E : the head of the malleus is compressed, its handle is bent. 

 In the Rhinoceros, also, the tympanic, which is reduced to the 

 frame of the membrane, is indistinguishable from the mastoid 

 and squamosal with which it early becomes fused. The petrosal 

 is very small. The stapes is triangular, with a moderate vacuity, 

 and thick crura, ib. F : the crura of the incus are very short : the 

 head of the malleus is bifid, its handle much curved. The conch 

 is pedunculate, and expands into a moderate elliptical chamber, 

 from the upper part of the head. The tympanic of Hyrax is 



