Biceps Brachii

Pectoralis Major 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. Deltoid 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. Biceps Brachii 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 elbow. 1-20 HM3F0128 MASSETER STERNOCLEIDO- MASTOID DELTOID PECTORALIS MAJOR BICEPS BRACHII ADDUCTOR LONGUS GRACILIS GASTROCNEMIUS SOLEUS TIBIALIS ANTERIOR VASTUS MEDIALIS VASTUS LATERALIS RECTUS FEMORIS QUADRICEPS SARTORIUS LATISSIMUS DORSI TRAPEZIUS Figure 1-28.—Anterior view of superficial skeletal muscles.