Figure 3-27.Important superficial muscles, anterior view.
and the occipital bone. They have their insertion
in the clavicle and scapula.
The LATISSIMUS DORSI is a broad flat
muscle that covers approximately one-third of the
back on each side. It rotates the arm inward and
draws the arm down and back. It originates from
the upper thoracic vertebrae to the sacrum and
the posterior portion of the crest of the ilium. Its
fibers converge to form a flat tendon that has its
insertion in the humerus.
The PECTORALIS MAJOR is the large
triangular muscle that forms the prominent chest
muscle. 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, ster-
num, and cartilages of the true ribs, and the ex-
ternal oblique muscle. Its insertion is in the greater
tubercle of the humerus.
The DIAPHRAGM is an internal muscle that
forms the floor of the thoracic cavity and the ceil-
ing of the abdominal cavity. It is the primary musc-
le of respiration, modifying the size of the thorax
and abdomen vertically. It has three openings for
the passage of nerves and blood vessels.
The DELTOID muscle raises the arm and has
its origin in the clavicle and the spine of the
scapula. 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 mus-
cle on the anterior surface of the upper arm. Its
origin is in the outer edge of the glenoid cavity
and its insertion in the tuberosity of the radius.
This muscle rotates the forearm outward (supina-
tion) and, with the aid of the brachial muscle,
flexes the forearm at the elbow.
The TRICEPS BRACHII is the primary ex-
tensor of the forearm (the antagonist of the biceps
brachii). It originates at two points on the
humerus and one on the scapula. These three
heads join to form the large muscle on the
posterior surface of the upper arm. The point of
insertion is the olecranon process of the ulna.
Figure 3-28.Important superficial muscles, posterior view.