Metacarpal.-The metacarpal bones are numbered one to five, corresponding with the five fingers, or digits, with which they articulate. The fingers are named as follows: 1st-thumb; 2nd-index; 3rd-middle; 4th-ring; and 5th-little.

Phalanges.-The small bones of the fingers are called phalanges, and each one of these bones is called a phalanx. Each finger has three phalanges, except the thumb (which has two). The phalanges are named for their anatomical position: The proximal phalanx is the bone closest to the hand; the distal phalanx is the bone at the end of the finger; and the middle phalanx is the bone located between the proximal and distal phalanges.

LOWER EXTREMITY.-The lower extremity includes the bones of the hip, thigh, leg, ankle, and foot. The bones that form the framework of the lower extremities are listed in table 1-2.

Figure 1-22.-Left arm: A. Frontal view of left arm with hand supinated; B. Frontal view of left arm with hand pronated.

Innominate.-The innominate bone, commonly known as the hip, is a large, irregularly shaped bone composed of three parts: the ilium, ischium, and pubis (fig. 1-23). In children these three parts are separate bones, but in adults they are firmly united to form a cuplike structure, called the acetabulum, into which the head of the femur fits. The ilium forms the outer prominence of the hip bone (the crest of the ilium, referred to as the iliac crest, provides an anatomical landmark above the ilium); the ischium forms the hard lower part; and the pubis forms the front part of the pelvis.

Symphysis Pubis.-The area where the two pubic bones meet is called the symphysis pubis and is often used in anatomical measurements. The largest foramen, or opening, is located in the hip bone, between the ischium and the pubis, and is called the obturator foramen (fig. 1-23). The crest of the ilium is used in making anatomical and surgical measurements (e.g., location of the appendix, which is approximately halfway between the crest of the ilium and the umbilicus).

Femur.-The femur, or thigh bone, is the longest bone in the body (fig. 1-24). The proximal end is rounded and has a head supported by a constricted neck

Figure 1-23.-Pelvic girdle.

Figure 1-24.-Anterior view of the right leg.

Table 1-2.-Bones of the Lower Extremities

that fits into the acetabulum. Two processes called the greater and lesser trochanters are at the proximal end for the attachment of muscles. The neck of the femur, located between the head and the trochanters, is the site on the femur most frequently fractured. At the distal end are two bony prominences, called the lateral and medial condyles, which articulate with the tibia and the patella.

Patella.-The patella is a small oval-shaped bone overlying the knee joint. It is enclosed within the tendon of the quadriceps muscle of the thigh. Bones like the patella that develop within a tendon are known as sesamoid bones.

Tibia.-The tibia, or shin bone, is the larger of the two leg bones and lies at the medial side. The proximal end articulates with the femur and the fibula. Its distal end articulates with the talus (one of the foot bones) and the fibula (fig. 1-25). A prominence easily felt on the inner aspect of the ankle is called the medial malleolus.

Fibula.-The fibula, the smaller of the two leg bones, is located on the lateral side of the leg, parallel to the tibia. The prominence at the distal end forms the outer ankle and is known as the lateral malleolus.

Tarsus.-The tarsus, or ankle, is formed by seven tarsal bones: medial cuneiform, intermediate cuneiform, lateral cuneiform, cuboid, navicular, talus, and calcaneus. The strongest of these is the heel bone, or calcaneus.

Metatarsus.-The sole and instep of the foot is called the metatarsus and is made up of five metatarsal bones (fig. 1-25). They are similar in arrangement to the metacarpals of the hand.

Phalanges.-The phalanges are the bones of the toes and are similar in number, structure, and arrangement to the bones of the fingers.