396 



STRIGlNiE, 



than the rest, and capable of covering the aperture. Within 

 this rim is an irregular cavity, having at its lower part a trans- 

 verse oblong aperture, the commencement of the passage that 

 leads to the membrane of the tympanum, on which the im- 

 pulses of the air impinge. In man and the mammalia this 

 passage, the meatus auditorius externus, is of considerable 

 length, but in birds extremely short, sometimes not more than 

 a twelfth of an inch. 



Fig. 23/. 



Now, in some Owls, for example the Snowy Owl and the 

 Hawk Owl, Strix nyctea of Linnseus, and Strix funerea of 

 Gmelin, the external ear differs from that of Hawks only in 

 being proportionally much larger. In these birds, it is of an 

 ellijitical form. Fig. 287, h, and its greatest diameter is not more 

 than from a third to a half of the height of the skull. In the 

 Eagle Owl, Strix Bubo of Linnaeus, the external ear is about 

 half the height of the skull, being an inch or a little more in 

 length, and nearly of the same form as in the Snowy Owl. In 

 both cases, it has the margins little elevated, and beset with slen- 

 der feathers. In several Asiatic species which I have examin- 

 ed, otherwise allied to the Eagle Owl, I have found the aper- 

 ture of the ear proportionally much smaller. In our common 

 Tawny Owl, Strix Aluco, it is of medium size, for that of an owl, 

 although in fact very large, Fig. 237, c, being more than half 

 the height of the skull, and has moreover an elevated anterior 

 semicircular flap or lid. Such an ear, having its margins elevat- 

 ed in whole or in part, bears some resemblance to the human ex- 

 ternal ear, which having by anatomists been likened to a shell, 



