SENSE ORGANS. 437 



under the control of the will. Lacrymal and harderian glands 

 are both present. They are placed within the orbit, the former 

 on the outer side of the eyeball and the latter on the inner and 

 upper side. The harderian gland opens within the nictitating 

 membrane. The secretion of both glands is carried off by a wide 

 lacrymo-nasal duct which leaves the inner angle and opens in the 

 nasal cavity immediately above the internal nares. 



The auditory organ is contained in the periotic bone. It 

 possesses three large semicircular canals which open into the utri- 

 cle, and a saccule which gives off a slightly bent cochlea (lagena) 

 and a ductus endolymphaticus ; the latter enters the cranial 

 cavity and ends in the dura mater in a flattened sac. The coch- 

 lea is without an organ of Corti. The vestibule has two 

 openings : the fenestra ovalis which is closed by the terminal 

 piece (operculum) of the columella and looks into the tym- 

 panic cavity, and a second more rounded opening, the 

 fenestra rotunda, which is closed by membrane only. The 

 eustachian tubes after leaving the bone join to form a short 

 membranous duct, which opens into the pharynx by a median 

 opening. The tympanic cavity also communicates with air- 

 spaces in the neighbouring bones of the skull. Externally the 

 tympanic cavity is closed by a tympanic membrane, to which 

 the long rod-shaped auditory ossicle (columella), corresponding 

 to the auditory ossicles of Mammalia, is fastened. On the outer 

 side of the tympanic membrane there is a short external audi- 

 tory meatus, the opening of which is often surrounded by a circle 

 of large feathers, and in the owls is overlapped by a cutaneous 

 valve which is likewise beset with feathers, and constitutes a 

 rudimentary pinna. 



The olfactory organ has three pairs of turbinal bones in the 

 spacious nasal cavities. The two nasal apertures,* except in 

 Apteryx, lie more or less near the root of the upper beak ; some- 

 times (crows) they are covered and protected by stiff hairs ; in 

 the Procellariidae they are elongated into a tube and join one 

 another. A so-called nasal gland usually lies on the frontal bone, 

 more rarely beneath the nasal bone or at the inner corner of the 

 eye ; it opens by a simple duct into the nasal cavity. 



The sense of taste is connected with the soft base of the tongue 



* In Phalacrocorax and apparently in other Steganopodidae the external 

 nostrils are said to be closed in the adult. 



