EAGLE PASS, a city of Texas, the county-seat of Maverick co. It is on the Southern Pacific and the Mexican Inter national railroads, and on the Rio Grande river. It is the center of an important coal mining, agricultural, and stock-raising region, has an extensive trade in cattle, hides, and wool, is a port of entry, and has a large international trade. It has a handsome Federal build ing. Pop. (1910) 3,536; (1920) 5,765.
EAR, the organ of hearing; is com posed of three parts, the external ear, the middle ear, or tympanum, and the internal ear, or labyrinth. The external ear consists of two portions, the auricle or pinna (the part popularly recognized as the ear), and the auditory canal or external meatus. In man, the auricle, on its outer or more exposed surface, presents various eminences and depres sions, resulting from the form of its particles of dust, and other small for eign bodies, and prevents their farther passage into the meatus.
The middle ear, or cavity of the tym panum, is a space filled with air which is received from the pharynx through the Eustachian tube and traversed by a chain of very small movable bones, which connect the membrane of the tympanum with the external ear. It lies, as its name implies, between the ex ternal meatus and the labyrinth or in ternal ear, and opens posteriorly into the cells contained in the mastoid por tion of the temporal bone, and ante riorly into the Eustachian tube. The cavity is of an irregular shape, and is lined by a very delicate ciliated epithe lium, which is a prolongation of that of the pharynx through the Eustachian tube. Its external wall is in great part formed by the membrane of the tympa num, which is nearly oval, and placed in a direction slanting inward, so as to form an angle of about 45° with the floor of the auditory canal.
The Eustachian tube, into which the tympanic cavity opens anteriorly, is about an inch and a half in length, and passes downward, forward, and into its opening in the pharynx. It is partly
osseus but chiefly cartilaginous, and al lows the free passage of air in and out of the tympanum.
The internal ear or labyrinth is the essential part of the organ of hearing, being the portion to which the ultimate filaments of the auditory nerve are dis tributed. It is composed of three parts: the vestibule, the semi-circular canals, and the cochlea, which form a series of cavities presenting a very complicated arrangement, and lying imbedded in the hardest part of the petrous portion of the temporal bone. They communicate externally with the tympanum through the fenestra ovalis, and the fenestra ro tunda; and internally with the internal auditory canal, which conveys the audi tory nerve from the cranial cavity to the internal ear. The very dense bone im mediately bounding these cavities is termed the osseous labyrinth, to distin guish it from the membranous labyrinth, which lies within a portion of it. The cochlea, so-called from its resemblance to a common snail-shell, consists of an osseous and gradually tapering canal, about an inch and a half in length, which makes two turns and a half spirally around a central axis, termed the modiolus, which is perforated at its base for the entrance of the filaments of the cochlear portion of the auditory nerve. This spiral canal gradually di minishes toward the apex of the cochlea. At its base it presents an opening into the vestibule, partially divided into two. In the infant state, one of these open ings (scala tympani) does not communi cate with the vestibule, but is closed by the membrane of the fenestra rotunda. Its interior is sub-divided into two pas sages (scale) by an osseous lamina. This is the lamina spiralis, which incom pletely divides the cochlea into an up per passage, the scala vestibuli, and a lower one, the scala tympani—that is, the division is incomplete so far as the skeleton goes, but is completed during life by the lamina spiralis membranacea (or basilar membrane).