306 ANATOMY OF THE DOMESTIC POWL 



The inner ear consists of a membranous labyrinth, surrounded by 

 a spongy bony structure the bony labyrinth. In it are recognized 

 the vestibulum, the three half-circle shaped canals, and the cochlea. 

 The superior semicircular canal is the largest. The acoustic nerve 

 enters at the end of the canals near the ampullae. The nerves are 

 supported in delicate vascular membranes lining the canals and 

 slightly projecting into the ampullae. 



The vestibulum is a small irregular cavity which communicates 

 with the arcades and the cochlea, and through the fenestra vesti- 

 bularis with the drum cavity. The endolymph of the vestibulum 

 contains microscopic crystals of calcium carbonate. The semi- 



FlG. 78. Diagram of the inner ear. I, The integument. 2, The superior 

 semicircular canal. 3, The external canal. 4, The horizontal canal. 5, The 

 ampulla. 6, The obtuse osseous conical cochlear cavity. 7, The Eustachian 

 tube. 8, The tympanum. 9, Filaments of the auditory nerve. 



circular canals are relatively larger and thicker than in mammals. 

 The ampullae in the upper and back part are separated by walls. 

 The cochlea is an obtuse conical tube-like structure slightly curved 

 at the blind extremity with the concavity directed backward. It 

 contains a membranous lining. At this point the cochlea is broad- 

 ened and accommodates a branch of the auditory nerve. This 

 nerve spreads out in fine filaments upon the surface of the tubes. 

 The hollow space of the cochlea is divided by a spiral partition, 

 making two chambers, the scala vestibuli and the scala tympani. 

 These walls extend from the beginning of the cochlea. 



The tympanic cavity is formed by the occipital, the basi- and ali- 

 sphenoids, the petrosal portion of the temporal bone. It represents 

 the stapedial canal leading to the foramen ovalis and the pneumatic 



