STEUCTUEE OF THE EAE. 737 



sure of the eyelids, and is continued into the nasal cavity, where it 

 terminates in front of the representative of the middle turbinated bone. 



(2087.) The second gland, the glandula Harderi, seems to supply 

 the place of the Meibomian glands of the human eyelids : it forms a 

 considerable glandular mass, situated behind the conjunctiva, at the 

 nasal angle of the eyelids ; and through its excretory duct, which opens 

 behind the nictitating membrane, the lubricating secretion that it fur- 

 nishes is poured out. 



(2088.) 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, however, is poured into the nose by 

 one or more ducts, and thus serves copiously to moisten the Schneide- 

 rian membrane. 



(2089.) The auditory apparatus of a Bird is almost precisely similar 

 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 fea- 

 thers around the ear are so 

 disposed as to collect faint 

 impressions of sound; and 

 in the Owls, besides possess- 

 ing a broad opercular flap, Organ of hearing in the Owl. 



that forms a kind of external ear, there are sinuosities, external to the 

 membrana tympani, which resemble, not very distantly, those found in 

 the ear of Man. 



(2090.) Entering into the composition of the organ of hearing in the 

 class before us, we have the membrana tympani (fig. 367, a), and tym- 

 panic cavity, from which a wide Eustachian tube (d) leads to the poste- 

 rior nares. The labyrinth presents the vestibule (c), the semicircular 

 canals (6), and the rudimentary cochlea (e) ; all of which so exactly 

 correspond in structure with what has already been described when 

 speaking of the ear of Reptiles ( 1997 et seqq.), as to render repetition 

 needless. A single trumpet-shaped bone, the representative of the 

 stapes, communicates immediately between the membrana tympani and 

 the fenestra ovalis ; but two or three minute cartilaginous appendages, 

 connected with the membranous drum of the ear, are regarded as being 

 the rudiments of the malleus, incus, and os orbiculare met with in the 

 next class. 



(2091.) The kidneys in the Bird (fig. 368, e e e) are very large ; they 



SB 



