The numerous vessels, nerves and visceral structures found in the neck make this region both interesting and important to the surgeon. The upper limits of the neck are the lower border of the jaw, a line extending from the angle of the jaw to the mastoid process, and the superior curved line of the occipital bone. The lower limits are the sternal notch, the clavicles and a transverse line from the acromioclavicular joint to the spinous process of the 7th cervical vertebra. The contour of the neck varies with age and sex, being well rounded in women and children but more angular in men; hence, the landmarks are more conspicuous in the male. In extension, the anterior part of the neck is lengthened, and in flexion it is shortened, so that the distance between its movable parts from the sternum to the lower jaw varies as does the relationship of these parts to the vertebrae. Therefore, it is necessary in giving relative positions of landmarks to suppose that the neck is midway between flexion and extension, this being the natural upright position unless otherwise stated. The anterior portion of the neck contains the respiratory tube (larynx and trachea) and the alimentary tube (pharynx and esophagus); the great vessels and nerves are located on the sides, and the posterior portion contains the cervical segment of the spine and surrounding musculature. The infrahyoid region extends from the hyoid bone above to the suprasternal notch below and is limited laterally by the anterior border of the sternocleidomastoid muscles.
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