Sternocleidomastoideus Muscle, Posterior View

Description

Running obliquely along the posterolateral neck, the paired sternocleidomastoideus (sternocleidomastoid) muscles are isolated in color from a posterior viewpoint, their posterior borders forming a sharp boundary with the more superficial trapezius as it descends to the shoulder girdle. Superiorly, each sternocleidomastoideus narrows toward its insertion on the mastoid process and lateral half of the superior nuchal line, sitting lateral to the midline cervical spinous processes. Medially, the cervical vertebral column provides the axial reference, while laterally the muscle contours relate to the superior fibers of trapezius and the slope of the shoulder, where the posterior triangle begins to read clearly in profile. Depth is implied by the grayscale musculature that would typically include splenius capitis and levator scapulae deep to the sternocleidomastoideus and trapezius. Posterior orientation matters because it clarifies the sternocleidomastoideus as a landmark for surface anatomy and for the boundaries of the posterior cervical triangle, where the spinal accessory nerve (CN XI) crosses toward trapezius and is exposed to iatrogenic injury. A short neck incision for lymph node biopsy or posterior triangle dissection can denervate trapezius, leading to shoulder droop and limited abduction, and this view helps you visualize why the nerve’s course is unforgiving. Torticollis and muscle spasm also make more sense when you appreciate the sternocleidomastoideus line of pull from the mastoid region toward the sternum and clavicle, even when the inferior attachments are out of frame. Use this artwork in gross anatomy teaching for neck triangles, in ENT and head and neck surgery texts discussing accessory nerve preservation, or in physical therapy materials addressing cervical rotation and lateral flexion mechanics. It also suits patient education on post-operative shoulder dysfunction after posterior triangle procedures. Anatomical accuracy verified by SciePro's Medical Advisory Board.