26o 



THE EVOLUTION OF MAN. 



The ear of Vertebrates develops in many important 

 points similarly to the eye and nose, but yet in other 

 respects very differently.^"^^ The organ of hearing of the 

 developed human being resembles that of other Mammals 

 in all essential particulars, and is especially simila^r to that of 

 Apes. As in the latter, it consists of two principal parts, an 

 apparatus for the conveyance of sound (external and middle 

 ear) and an apparatus for producing the sensation of sound 

 (internal ear). The outer ear opens in the ear-shell {conclta 



Fio. 244. — Auditory organ of man (left ear, seen from the front; natnral 

 size) : a, ear-shell : b, exteraal ear-canal ; c, drum, or tympanic membrane i 

 d, cavity of drum ; e, ear-trumpet; /, g, h, the three ear honelets (/, hammer ; 

 g, anvil ; h, stirrup) ; i, ear-pouch (utriculus) ; Tc, the three semi-circular 

 canals ; I, ear-sac (sacculus) ; m, snail {cochlea) ; n, auditory nerve. 



auris), situated at the side of the head (Fig. 22-i, a). From 

 this the outer ear-canal, which is usually about an inch long, 

 leads to the insid.-^ of the head (h). The inner end of thia 





