Figure 3-29.The skin.
The GLUTEALS (MAXIMUS, MINIMUS,
and MEDIUS) are the large muscles of the but-
tocks, which extend and laterally rotate the thigh,
as well as abduct and medially rotate it. They arise
from the ilium, the posterior surface of the lower
sacrum, and the side of the coccyx. Their points
of insertion include the greater trochanter and the
gluteal tuberosity of the femur. The gluteus max-
imus is the site of choice for massive intramuscular
The QUADRICEPS is a group of four
muscles that make up the anterior portion of the
thigh. The rectus femoris originates at the ilium;
the vastus femoris, v. lateralis, and v. intermedius
originate along the femur. All four are inserted
into the tuberosity of the tibia through a tendon
passing over the knee joint. The quadriceps serves
as a strong extensor of the leg at the knee and
flexes the thigh.
The SARTORIUS is the longest muscle in the
body. It extends diagonally across the front of the
thigh from its origin at the ilium, down to its in-
sertion near the tuberosity of the tibia. Its func-
tion is to flex the thigh and rotate it laterally, and
to flex the leg and rotate it slightly medially.
The GRACILIS is a long slender muscle
located on the inner aspect of the thigh. It adducts
the thigh and flexes and medially rotates the leg.
Its origin is in the symphysis pubis, and its inser-
tion is in the medial surface of the tibia, below
The BICEPS FEMORIS (often called the
hamstring muscle) originates at the tuberosity of
the ischium and the middle third of the femur.
It is inserted on the head of the fibula and the
lateral condyle of the tibia. It acts, along with
other related muscles, to flex the leg at the knee
and to extend the thigh at the hip joint.
The GASTROCNEMIUS and SOLEUS (calf
muscles) extend the foot at the ankle. The
gastrocnemius originates at two points on the
femur; the soleus originates at the head of the
fibula and the medial border of the tibia. Both
are inserted in a common tendon called the
calcaneus, or Achilles tendon.
The TIBIALIS ANTERIOR originates at the
upper half of the tibia and inserts at the first
metatarsal and cuneiform bones. It flexes the foot.
THE INTEGUMENTARY SYSTEM
The skin, or integument, is the outer cover-
ing of the body. It consists of two layers, the
epidermis and the dermis, and supporting struc-
tures and appendages (fig. 3-29).
The skin covers almost every visible part of
the human body. Even the hair and nails are
outgrowths from it. It protects the underlying
structures from injury, drying, and invasion by
foreign organisms; it contains the peripheral end-
ings of many sensory nerves; and it has limited
excretory and absorbing powers. It also plays an
important part in regulating body temperature.
In addition, the skin is a waterproof covering that
prevents excessive water loss, even in very dry