44O MANUAL OF ZOOLOGY. 



which sounds can be collected and transmitted to the internal 

 ear. In some birds, however, as in the Ostrich and Bustard, 

 the external meatus auditorius is surrounded by a circle of 

 feathers, which can be raised and depressed at will. The ex- 

 ternal nostrils in Birds are usually placed on the sides of the 

 upper mandible, near its base, in the form of simple perfora- 

 tions, which sometimes communicate from side to side by the 

 deficiency of the septum narium. In the singular Apteryx of 

 New Zealand the nostrils are placed at the extreme end or tip 

 of the elongated upper mandible. Sometimes the nostrils are 

 defended by bristles, and sometimes by a scale (Rasores). 

 Taste must be absent, or almost absent, in the great majority 

 of birds, the tongue being nothing more than a horny sheath 

 surrounding a process of the hyoid bone, and serving for deglu- 

 tition or to seize the prey. In the Parrots, however, the 

 tongue is thick and fleshy, and some perception of taste may 

 be present. Touch or tactile sensibility, too, as already re- 

 marked, is very poorly developed in Birds. The body is 

 entirely, or almost entirely, covered with feathers ; the anterior 

 limbs are converted into wings, and rendered thereby useless 

 as organs of touch ; and the posterior limbs are covered with 

 horny scales or feathers. The bill certainly officiates as an 

 organ of touch, but it cannot possess any acute sensibility, as 

 in most birds it is encased in a rigid horny sheath. In some 

 birds, however, such as the common Duck, the texture of the 

 bill is moderately soft, and it is richly supplied with filaments 

 of the fifth nerve ; so that in these cases the bill doubtless con- 

 stitutes a tolerably efficient tactile organ. The " cere," too, 

 or the fleshy scale found at the base of the bill in some birds, 

 is in all probability also used as a tactile organ. 



The last anatomical peculiarity of Birds which requires 

 notice is the peculiar apparatus known as the " inferior 

 larynx," by which the song of the singing birds is conditioned. 

 "The air-passages of birds commence by a simple superior 

 larynx, from which a long trachea extends to the anterior 

 aperture of the thorax, where it divides into the two bronchi, 

 one for each lung. At the place of its division there exists in 

 most birds a complicated mechanism of bones and cartilages, 

 moved by appropriate muscles, and constituting the true organ 

 of voice; this part is termed the inferior larynx." (Owen.) 

 The structure of the vocal apparatus is extremely complicated, 

 and there is no necessity for entering upon it here. It is to be 

 remembered, however, that those modifications of the voice 

 which constitute the song of birds, are produced in a special 

 and complex cavity placed at the point where the trachea 



