MUSCLES OF THE

NECK (fig. q)  .—Just below the mandible is the CRANIAL; and NERVE, SPINAL) . The posterior triangle is formed digastric, which, as its name shows, has two bellies and a central by the sterno-mastoid in front, the trapezius behind, and the clavicle tendon; the anterior belly, supplied by the fifth nerve, is attached to below; in its floor from above downward part of the following muscles the mandible near the symphysis, the posterior supplied by the are seen: corn plexus, splenius, levator anguli scapulae, scalenus 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-hyoid 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 shoulder, 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 anterior 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 omo-hyoid muscle rises from the upper border of the scapula and runs across medius and scalenus anticus . Sometimes a small piece of the scalenus posticus is caught sight of behind the scalenus medius . The splenius rotates the head to its own side, the levator anguli scapulae raises the upper angle of the scapula, while the three scalenes run from the transverse processes of the cervical vertebrae 'and fix or raise the upper ribs . The trapezius (fig . 5) arises from the spines of the thoracic vertebrae and the ligamentum nuchae, and is inserted into the outer third of the clavicle and the spine of the scapula; it is used in shrugging the shoulders and in drawing the upper part of the scapula toward the mid-dorsal line . Its nerve supply is the spinal accessory and third and fourth cervical nerves .

When the superficial muscles and complexus are removed from the back of the neck, the sub-occipital triangle is seen beneath the occipital bone .