HEAD AND NECK.] T M Y 837 lower fibres alone of the orbicularis contract, and the lower lid is elevated. The elevation of the upper lid, as in opening the eye, is due to the levator palpebr* superioris, which, arising within the orbit, is inserted into the upper eyelid. Muscles are inserted into the framework of the nostrils so as to increase or diminish the size of their orifices, and thus to promote or impede the passage of air into the nose. The size of the orifice is increased by two elevator muscles inserted into the ala, or side of the nostril ; and when violent exercise is being performed, or respiration is from any cause impeded, the nostrils are always widely dilated. One of these elevator muscles, which also sends a slip down to the upper lip, and is con sequently called the common elevator, is the muscle by the contraction of which a sneer is expressed. A partial closure of the nostril can be effected by small muscles which depress and compress the alse of the nose : in man these muscles are rudimentary as compared with the seal and other aquatic mammals, in which a powerful sphincter muscle closes the nostrils in the act of diving. The lips can be elevated or depressed so as to close or open the mouth ; they can be protruded or retracted, or the corners of the mouth can be drawn to one side or the other, by the action of various muscles which are inserted into these movable folds of the integument. The orbicularis oris is a sphincter muscle, the fibres of which lie both in the upper and lower lips; by its contraction the mouth is closed and the lips pressed against the teeth, as when a firm resolution is intended to be expressed. The mouth is opened by the elevator muscles of the upper and the depressors of the lower lip ; it is transversely elon gated by the zygomatic and risorius muscles, which pass to its corners, and which are brought into action in the acts of smiling and laughing. But the muscles of the lips also play an important part in connection with the reception of food into the mouth, and with the act of articula tion. The cavity of the mouth forms the commence ment of the ali mentary canal, and is lined by a soft mucous mem brane. In it the teeth and tongue are situated, and into it the secre tion called saliva is poured. It opens behind into the pharynx. The side walls of the mouth are called the cheeks, and into the formation of each cheek a flattened quadrila teral muscle, the buccinator, enters. This muscle is at tached above and below to the upper and lower jaw bones, behind to FIG. 20. Profile of cheek and pharynx, a, buccinator; 6, tensor; c, levator palati; d, ,/, superior, middle, and inferior constrictors; g, thyro-hyoid; h, hyo- glossus; ;, mylo-hyoid; m, crico-thyroid; n, stylo- pliaryngeus; o, stylo-glogsus; q, fibrous band which pives origin to buccinator and superior constrictor; 1, glosso-pharyngeal nerve; 2, superior laryngeal artery; 3, superior laryngeal nerve; 4, its branch to crico-thyroid; 5, inferior laryngeal nerve and artery. a fibrous band, to which the upper constrictor muscle is also connected, so that the walls of the mouth and pharynx are continuoua with each other, whilst in front the buccinator blends with the structures in the lips. It compresses the cheeks, and drives the air out of the cavity of the mouth as in playing a wind instru ment ; hence the name, " trumpeter s muscle." The aperture of communication between the mouth and pharynx is named the isthmus of the fauces. It is bounded below by the root of the tongue, on each side by the tonsils, and above by the soft palate. The soft palate is a structure which hangs pendulous from the posterior edge of the hard bony palate. From its centre depends an elongated body, the uvula, and from each of its sides two folds extend, one downwards and forwards to the tongue, the other down wards and backwards to the pharynx. These folds are called the anterior and posterior pillars of the fauces or palate. Between the anterior and posterior pillar, on each* side, the tonsil is seated. The soft palate and its pillars are invested by the mucous lining of the mouth and pharynx, and contain small but important muscles. The muscles of the soft palate and uvula, termed the elevators and tensors, raise and make them tense during the process of deglutition. The muscles of the posterior pillars, or palato-pharyngei, by their contraction, approximate the walls of the pharynx to the soft palate and uvula, whilst the muscles of the anterior pillars, or palato-glossi, diminish the size of the fauces. The pharynx is a tube with muscular walls, lined by a Muscles mucous membrane, which communicates above and in front pharynx with the cavities of the nose, mouth, and larynx, whilst below it is continuous with the oesophagus or gullet. It serves as the chamber or passage down which the food goes from the mouth to the oesophagus in the act of swallowing, and through which the air is transmitted from the nose or mouth to the larynx in the act of breathing. It lies immediately behind the nose, mouth, and larynx, and in front of the five upper cervical verte brae. Its length is from 4J to 5% inches ;its widest part is opposite the back of the mouth. The prin cipal muscles in its walls are call ed the constric tors, and are named, from above down wards, superior, middle, and in ferior. They are arranged in pairs, and arise from the cartil ages of the larynx, from the hyoidbone,lower jaw, and internal pterygoid pro- _ J . , *, FIG. 21. Interior of the pharynx, seen by opening its CeSS 01 tile SpllC- posterior wall, a, a, Eustaehian tube; 6, 6, tensor; f, n m rl ivl-nlaf f lin levator palati ; d, leva.tor uvulse ; e, , palato-pharyngeu= ; noia, mist - /; pa i ato . glOMUS . ffi A% A< the three constrictors . ;, ton- superior also is. springs from the fibrous band to which the buccinator is attached ; their fasciculi curve backwards to the middle line of the posterior wall of the pharynx, to be inserted into a tendinous band which extends longitudinally along this wall of the tube. The action of the muscles of the mouth, palate, and
pharynx may now be considered in connection with the
