608 



TEXTBOOK OF ZOOLOGY 



chorioid just beneath, and ttie membranous retina lining the inside 

 of the posterior portion. The crystalline lens is of a soft texture, is 

 nearly round, and is enclosed in a capsule. The cornea is of a horny 

 consistency and is transparent. Light thus passes rapidly through 

 it to the posterior part of the eye. There is a comb-shaped membrane 

 stretching from the entrance of the optic nerve at the posterior wall of 

 the eye to the posterior surface of the lens. This structure is called 

 the pecten, and it is supposed that it has something to do either with 

 the nutrition of the eye or with the keen accommodation possessed by 

 the bird. The chicken has a lacrimal duct and sheds tears. 



- — y^ 



OLFACTORY NERVES 

 OLFACTORY LOBES 



CEREBRAL LOBES 



LEFT OPTIC LOBE 



PINEAL BODY 

 CEREBELLUM 

 TRIGEMINAL N. 



-FACIAL N. 

 -AUDI TORY N. 

 -MEDULLA OBLONGATA 



Fig. 324. — Dorsal view of brain of chicken. (Drawn by Titus Evans.) 



The organ of hearing is embedded in the skull and consists of the 

 external meatus, tympanic membrane, one ossicle membrane, and the 

 columella which is attached to the tympanic membrane by a cartilage. 

 The inner ear is enclosed in the bony labyrinth and contains the 

 vestibule, three semicircular canals, and the membranous cochlea. The 

 cochlea has arisen from a pocketlike lagena on the vestibule, and is 

 much better perfected in birds than in simpler vertebrates. The 

 Eustachian tube provides a connection between the tympanic cavity 



