FIG. 78.—Diagram of the inner ear. 1, 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. ] The =vestibulum= is a small irregular cavity which communicates with the arcades and the cochlea, and through the fenestra vestibularis with the drum cavity. The endolymph of the vestibulum contains microscopic crystals of calcium carbonate. The semicircular canals are relatively larger and thicker than in mammals. The ampullæ 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 broadened 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 alisphenoids, the petrosal portion of the temporal bone. It represents the stapedial canal leading to the foramen ovalis and the pneumatic apertures by which the air from the Eustachian tube is conducted to the precranial diploë. THE ORGAN OF SMELL The nose is the seat of the peripheral portion of the organ of the sense of smell. The terminals of the olfactory nerves, which receive the impressions of odors, are broadened in the mucous membrane of the walls of the anterior nares. There are no ethmoidal volutes, or sieve-like structure, in birds. The nerve extends from the anterior portion of the brain in cone-shape, finally dividing into filaments which are distributed over the mucous surface of the turbinated bones. THE ORGAN OF TASTE The most important part of the organ of taste is the _tongue_. In birds the dorsum of the tongue is covered by a thick stratum corneum, a heavy layer of stratified squamous epithelium. The tongue, therefore is not in birds so well adapted for the perception of taste as it is in mammals. The lingual branch of the trigemini is lacking in birds. This fact makes the ninth pair, or the nervi glosso-pharyngei, the exclusive nerves of taste. There is an opinion ventured by one anatomist that, since the first and the second branch of the fifth pair, or trigemini, have terminal filaments in the hard palate, they may furnish fibers for the sense of taste. There are many taste cells on the tongue and on the dorsal palate. THE ORGAN OF TOUCH The peripheral parts of the organ of touch in the fowl are the skin and the feathers.