OSTEOLOGY 49 



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 

 vertebrae, forms the roof of the pelvic cavity. It articulates at its 

 inner border with the lumbo-sacral vertebrae, 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 

 vertebrae 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 vertebrae by the sutura ilio-lumbalis, and to the transverse 

 processes of the last sacral vertebrae 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. 



Description. The ischium is smaller than the ilium and is a 

 flattened, triangular-shaped bone, thickest where it forms the 

 posterior part of the acetabulum, becoming thinner and broader as 

 it extends backward. Posteriorly it forms the caudal extension. 

 The inferior border is turned slightly outward and is fused with the 

 pubis. Between these bones there is located the large oval ischiadic 

 foramen, through which passes the ischiadic nerve. This bone aids 

 the ilium in the formation of the obturator foramen through which 

 passes the tendon of the internal obturator muscle. The lower 

 part of the ischium which separates the ischiadic foramen from the 

 obturator foramen is called the ramus ascendens ossis ischii. 



