The fovea lumbalis contains the anterior lobe of the kidney, and is circumscribed anteriorly by the last rib-carrying vertebra, and posteriorly by the transverse process of the last lumbar vertebra. In the fovea ischiadica which follows, lie the nerve plexus ischiadicus and the middle lobe of the kidney. Its posterior boundary is the linea arcuata. The linea arcuata is a line drawn from the acetabulum of the one side to the acetabulum of the other side. The fovea pudendalis contains the posterior lobe of the kidney. The posterior boundary is the anterior border of the first coccygeal vertebra. It gives passage to the nerve plexus pudendo-hemorrhoidalis. The ilium, the ischium, and the pubis join to form the cotyloid cavity, or acetabulum, in which articulates the head of the femur. The floor of the cavity is perforated by a relatively large round foramen. =The Ilium.= _Location._—The ilium, together with the lumbo-sacral vertebræ, forms the roof of the pelvic cavity. It articulates at its inner border with the lumbo-sacral vertebræ, postero-laterally with the ischium and at the cotyloid cavity with the pubis. _Description._—The ilium is remarkable for its development in the long axis of the vertebral column. It is long and narrow; and mesially, where it is thickest it forms the upper wall of the acetabulum. Anterior to the acetabulum it is outwardly concave, and posterior to the acetabulum it is convex. The ilium fuses with the last dorsal vertebra and with the lumbo-sacral vertebræ and is excavated on its internal face. This surface is irregular and lodges the kidneys. This inner margin of the renal part enters with the square extensions of the posterior excavation passing into the posterior iliac spine. The external margin is the extension of the crista transversa and forms the _processus ischiadicus_. Posteriorward the renal part of the ilium joins the ischium. The ilia converge at the summits of the anterior sacral spines forming the _ilio-lumbar_ spines. The ilium is joined to the square extensions of the last sacral vertebra by the _symphysis ilio-sacralis_, to the larger part of the lumbar vertebræ by the _sutura ilio-lumbalis_, and to the transverse processes of the last sacral vertebræ by the _symphysis ilio-sacri_. =The Ischium.= _Location._—The ischium is located in the postero-inferior part of the pelvis. It joins superiorly with the ilium, and inferiorly with the pubis.