Muscles of the Neck and Trunk

Muscles That Move the Head 
Sternocleidomastoid muscles occur in the sides of the neck and extend from the sternum to the mastoid process (they are named for their attachments). When both of these muscles contract, the neck is flexed and the head is bent toward the chest. When only one contracts, the head turns to the opposite side.
Each trapezius muscle is triangular, but together, they take on a diamond or trapezoid shape. A trapezius muscle extends from the base of the skull down to the end of the thoracic vertebrae and inserts on a scapula laterally. The trapezius muscles extend the neck and help move the scapulae when the shoulders are shrugged or pulled back.
The sternocleidomastoid muscles and trapezius muscles are antagonistic because the sternocleidomastoid muscles flex the neck, and the trapezius muscles extend it.
Muscles of the Trunk 
External and internal obliques, and the transversus abdominis are located in the abdominal wall. The ex­ternal and internal obliques occur on a slant and are at right angles to one another between the lower ribs and the pelvic girdle. Below the obliques, the transversus abdominis extends horizontally across the abdomen. As with plywood, the abdominal wall is strengthened by having muscle fibers that run in differ­ent directions. All of these muscles tense and support the abdominal wall.
Rectus abdominis has a straplike appearance but takes its name from the fact that it runs straight (rectus means straight) up from the pubic bones to the ribs and ster­num. It is the outermost muscle that compresses the contents of the abdominal cavity, but it also helps flex the vertebral column.
The obliques (external and internal), the transversus abdominis, and the rectus abdominis all function to provide a sturdy abdominal vvall.