The pectoralis major is the large triangular muscle
that forms the prominent chest muscle (fig. 1-28). It
rotates the arm inward, pulls a raised arm down toward
the chest, and draws the arm across the chest. It
originates in the clavicle, sternum, and cartilages of the
true ribs, and the external oblique muscle. Its insertion
is in the greater tubercle of the humerus.
The deltoid muscle raises the arm and has its origin
in the clavicle and the spine of the scapula (figs. 1-28
and 1-29). Its insertion is on the lateral side of the
humerus. It fits like a cap over the shoulder and is a
frequent site of intramuscular injections.
The biceps brachii is the prominent muscle on the
anterior surface of the upper arm (fig. 1-28). Its origin
is in the outer edge of the glenoid cavity, and its
insertion is in the tuberosity of the radius. This muscle
rotates the forearm outward (supination) and, with the
aid of the brachial muscle, flexes the forearm at the
Figure 1-28.Anterior view of superficial skeletal muscles.