23-2 ANATOMY OF VERTEBRATES. 



membrane, which is placed very obliquely. In the pangolins 

 {Manis) the ear-conch is presented by a small scale-like fold of 

 thin integument. 



o 



Iii the Elephant the petrosal is small in proportion to the 

 size of the animal : its apex is grooved by the entocarotid. The 

 post-tympanic part of the mastoid meets the postglenoid process 

 below and circumscribes the outer auditory aperture : the tym- 

 panic contributes the lower wall of the meatus, internal to which 

 it expands into a ' bulla,' which unites with the petrosal. The 

 tympanic cavity communicates with the air-sinuses so extern 

 sively developed in the cranium, fig. 154. The stapes, fig. 

 175, G, has a -thin convexo-concave base; its branches are of un- 

 equal length ; the incus and malleus are large in proportion : the 

 drum-membrane is a full oval, the radiating fibres of its proper 



A 



Stapes, in Ungulata. 

 A. Hippopotamus. B. Hog. c. Musk Ox. D. Horse. E. Tnpir. F. Rhinoceros. G. Elephnnt. 



tunic diverge from the end and sides of the handle of the malleus, 



C5 



which, terminating near the great end of the oval, causes a cor- 

 responding difference in the length of these fibres. The ear- 

 conch is large, prodigiously so in the African species, and ex- 

 tremely mobile in both kinds. 



In the Hippopotamus the free part of the petrosal is of a 

 compressed pyriform figure ; the tympanic is expanded, at the 

 cavity, and prolonged obliquely and almost vertically upward 

 into a meatal tube, which becomes almost concealed between the 

 zygomatic and paroccipital in the old animal. The otosteals are 

 small and massive ; the stapes has a very small perforation, fig. 

 175, A; the handle of the malleus is short: the conch is very 

 small and little prominent. 



The petrosal is small and rounded in the Hog-tribe ; it retains 

 its primitive individuality in the Babyroussa ; not coalescing 

 with the independently developed mastoid or other elements of the 

 otocrane. The tympanic contains air-cells and is produced into 

 a long and narrow auditory canal obliquely upward and back- 

 ward, with an external orifice smaller than the frame of the 

 ear-drum. Both the base and aperture of the stapes are small, 

 fig. 175, B, and both the handle and body of the malleus are short. 



