(Pl. I.-2).—Just below the mandible is the digastric, which, as its name shows, has two bellies and a cen tral tendon ; the anterior belly, supplied by the fifth nerve, is attached to the mandible near the symphysis, the posterior sup plied by the seventh of the mastoid process, while the central tendon is bound to the hyoid bone. Stretching across from one side of the lower jaw to the other and forming a floor to the mouth is the mylo-/iyoid muscle; posteriorly this reaches the hyoid bone, and in the mid-line has a tendinous raphe separating the two halves of the muscle. Rising from the manubrium sterni and inner part of the clavicle is the sterno-cleido-mastoid, which is inserted into the mastoid process and superior curved lines of the occipital bone; when it contracts it makes the face look over the opposite shoul der, and it is supplied by the spinal accessory nerve as well as by branches from the cervical plexus. It is an important surgical landmark, and forms a diagonal across the quadrilateral outline of the side of the neck, dividing it into an anterior triangle with its apex downward and a posterior with its apex upward. In the an terior triangle the relative positions of the hyoid bone, thyroid cartilage and sternum should be realized, and then the hyo-glossus, thyro-hyoid, sterno-hyoid and sterno-thyroid muscles are explained by their names. The onio-hyoid muscle rises from the upper bor
der of the scapula and runs across both triangles to the hyoid bone. Where it passes deep to the sterno-mastoid it has a central tendon which is bound to the first rib by a loop of cervical fascia.
Rising from the styloid process are three muscles, the stylo-glos sus, stylo-hyoid and stylo-pharyngeus, the names of which indi cate their attachments. Covering these muscles of the anterior triangle is a thin sheet, close to the skin, called the platysma, the upper fibres of which run back from the mouth over the cheek and are named the risorius (Pl. 1.–i); this sheet is one of the few remnants in man of the skin musculature or panniculus carnosus of lower mammals. With regard to the nerve supply of the anterior triangle muscles, all those which go to the tongue are supplied by the hypoglossal or twelfth cranial nerve, while the muscles below the hyoid bone are apparently supplied from this nerve but really from the upper cervical nerves (see NERVE, CRANIAL ; and NERVE,