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   a n d   s u rg i c a l 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 1-14 HM3F0123 ILIAC CREST SACRUM ACETABULUM OBTURATOR FORAMEN SYMPHYSIS PUBIS ISCHIUM COCCYX ILIUM Figure 1-23.—Pelvic girdle. GREATER TROCHANTER LESSER TROCHANTER FEMUR PATELLA FIBULA TIBIA METATARSALS PHALANGES TARSAL HM3f0124 Figure 1-24.—Anterior view of the right leg. BONE COMMON NAME TOTAL NUMBER IN BODY innominate hip bone 2 femur thigh bone 2 patella knee cap 2 tibia leg bone 2 fibula leg bone 2 tarsals ankle bones 14 metatarsals foot bones 10 phalanges toe bones 28 Table 1-2.—Bones of the Lower Extremities