23G 



ANATOMY OF VERTEERATES. 



circular canal, and meeting the latter just before its junction 

 with the hinder semicircular canal. The stapes in lemurs is a 

 more equilateral triangle, and the perforation is less than in 

 monkeys : the incus has a longer and larger body in proportion 

 to its crura : the malleus has a shorter process, fig. 177, a. 



In Cebidce, ib. B, the stapes gains in length, but not much in 

 vacuity : the crura of the incus are still short, and the extensions 



Cebus. Cercopithecus. Homo. 



Otosteals, Quadrumana and Man. 



of the malleus are short in proportion to the mass articulating 

 Avith the incus. The tympanum is large ; the external meatus 

 short and very wide. In catarrhine monkeys, ib. C ( Cercopi- 

 thecus sabceus) and in apes a nearer approach is made to the 

 proportions and shapes of the human otosteals. 



There is a wider range of diversity in the external ear than in 

 the more essential parts of the organ. In the nocturnal Aye-aye, 

 in which the conch is relatively largest, there is a beginning of 

 the helix above the meatal fossa, but the rest of the margin is 

 thin and unfolded : the tragus is not very prominent, the anti- 

 tragus is better marked : a low fold represents the ' lower crus ' 

 of the anthelix, the upper one and the rest of that fold are 

 wanting. It is only in the orangs and chimpanzees that the 

 parts defined in the human auricle are represented. The free 

 margin is reflected to form a ' helix,' but not to the same degree 

 as in Man : the ' anthelix,' beginning above with both ( upper ' 

 and ' lower ' crus, is continued to the antitragus ; both scaphoid 

 navicular fossa? are defined, as well as the cavity of the concha 

 and the tragus : the lobulus is not pendant as in Man. In the 

 chimpanzee ( Troglodytes niger) the external ear is larger abso- 

 lutely than in the great gorilla ( Troglodytes Gorilla). 



In all the figures of the otosteals previously given the stapes is 

 drawn at right angles to its natural position, in which only a fore- 

 shortened view of the bone could be had, as in fig. 178, where it 

 is shown with its base a applied to the ' fenestra ' of the vestibule. 



