614 AVES BIRDS. 



apparatus is, of course, indispensable ; and, accordingly, birds are 

 supplied with two distinct glands, one being appropriated to the 

 secretion of tears, while the other furnishes a lubricating fluid, appa- 

 rently destined to facilitate the movements of the membrana nic- 

 titans. 



The lacrymal gland is situated, as in Man, at the outer angle 

 of the eye, and its duct pours the lacrymal secretion upon the eye- 

 ball near the external canthus. The lacrymal canal, whereby the 

 tears, after moistening the cornea, are discharged into the nose, 

 commences by two orifices (j^g*. 280, A, c) situated just behind the 

 internal commissure of the eye-lids ; and is continued, into the nasal 

 cavity, where it terminates in front of the representative of the 

 middle turbinated bone. 



The second gland, the glandula Harden, seems to supply the 

 place of the Meibomian glands of the human eye-lids : it forms 

 a considerable glandular mass, situated behind the conjunctiva at 

 the nasal angle of the eye-lids ; and through its excretory duct, 

 which opens behind the nictitating membrane, the lubricating secre- 

 tion that it furnishes is poured out. 



(683.) Besides the secreting organs above described, a third very 

 large gland is found, generally lodged in a depression beneath 

 the vault of the orbit, although in some genera it is situated 

 external to that cavity : the secretion of this gland is, however, 

 poured into the nose by one or more ducts, and thus serves copi- 

 ously to moisten the Schneiderian membrane. 



(684.) The auditory apparatus of a Bird is almost precisely si- 

 milar in its structure to that of one of the more perfect Reptiles, 

 such as the Crocodile. There is still no external ear, or osseous 

 canal worthy of being called an external meatus, yet in a few 

 rare instances, such as the Bustard, the feathers around the ear are 

 so disposed as to collect faint impressions of sound ; and in the 

 Owls, besides possessing a broad opercular flap, that forms a kind 

 of external ear, there are sinuosities, external to the membrana tym- 

 pani, which resemble, not very distantly, those found in the ear 

 of Man. 



Entering into the composition of the organ of hearing in the 

 class before us, we have the membrana tympani (Jig. 281, a), and 

 tympanic cavity, from which a wide Eustachian tube (d) leads to the 

 posterior nares. The labyrinth presents the vestibule (c), the semi- 

 circular canals (b), and the rudimentary cochlea (e); all of which 

 so exactly correspond in structure with what has already been de- 



