232 OSTEOLOGY. 



of the iliac fossa will be seen to be formed of but a thin layer of bone. A nutrient 

 foramen of large size is seen piercing the bone towards the posterior part of the 

 fossa. Below and behind the ilio-pectineal line the medial surface of the ilium 

 forms a small portion of the wall of the pelvis minor ; the bone here is smooth, and 

 rounded off posteriorly into the greater sciatic notch, where it becomes confluent with 

 the medial aspect of the ischium. This part of the bone is proportionately longer 

 in the female than in the male, and forms with the ischium a more open angle. 

 Just anterior to the greater sciatic notch there are usually the openings of one or 

 two large vascular foramina. From this surface arise some of the posterior fibres 

 of the obturator internus muscle. 



The ischium constitutes the lower and posterior part of the hip bone. 

 Superiorly its body (corpus) forms somewhat more than the inferior two-fifths of 

 the acetabulum together with the bone supporting it behind and medially. Below 

 this, the superior ramus passes downwards and backwards as a stout three-sided 

 piece of bone, from the inferior extremity of which a compressed bar of bone, called 

 the inferior ramus, extends forwards at an acute angle. This latter unites in front 

 and above with the inferior ramus of the pubis, and encloses the aperture called 

 the obturator foramen. 



Superiorly, and on the lateral aspect of the ischium, the acetabular surface is 

 separated from the bone below by a sharp and prominent margin, which is, 

 however, deficient in front, where it corresponds to the acetabular notch (O.T. cotyloid 

 notch) leading into the articular hollow; the floor of this notch is entirely 

 formed by the ischium. Below the prominent acetabular margin there is a 

 well-marked groove in which the obturator externus lies. Beneath this the 

 antero-lateral surface of the superior and inferior rami furnishes surfaces for the 

 attachments of the obturator externus, quadratus femoris, and adductor magnus 

 muscles. The postero-lateral surface of the ischium forms the convex surface on 

 the back of the acetabulum. The medial border of this is sharp and well defined, 

 and is confluent above with the border of the ilium, which sweeps round the greater 

 sciatic notch. From this border, on a level with the lower edge of the acetabulum, 

 there springs a pointed process, the spina ischiadica (ischial spine), to which are 

 attached the sacro - spinous ligament and the superior gemellus muscle. 

 Inferior to this, the postero-lateral surface narrows rapidly, its medial border 

 just below the spine being hollowed out to form the incisura ischiadica minor (lesser 

 sciatic notch). The lower part of this surface and the angle formed by the two 

 rami are capped by an irregularly rough piriform mass called the tuber ischiadicum 

 (ischial tuberosity). This is divided by an oblique ridge into two areas, the upper and 

 lateral for the tendon of origin of the semimembranosus muscle, the lower and medial 

 for the conjoined heads of the biceps and semitendinosus muscles. Its prominent 

 medial lip serves for the attachment of the sacro-tuberous ligament, whilst its 

 lateral edge furnishes an origin for the quadratus femoris muscle ; in front and 

 below, the adductor magnus muscle is attached to it. 



The medial surface of the body and superior ramus of the ischium form in part 

 the wall of the pelvis minor. Smooth and slightly concave from before backwards, 

 and nearly plane from above downwards, it is widest opposite the level of the ischial 

 spine. Below this, its posterior edge is rounded and forms a groove leading to the 

 lesser sciatic notch, along and over which the tendon of the obturator internus 

 passes. To part of this surface the fibres of the obturator internus are attached, 

 whilst the medial aspect of the spine supplies points of origin for the coccygeus and 

 levator ani muscles, as well as furnishing an attachment to the " white line " of the 

 pelvic fascia. The medial surface of the inferior ramus of the ischium is smooth, 

 and so rounded that its' inferior edge tends to be everted. To this, as well as to its 

 margin, is attached the crus penis, together with the ischio-cavernosus, obturator 

 internus, transversus perinei, and sphincter muscle of the membranous urethra. 

 In the female, structures in correspondence with these are found. 



The anterior part of the hip bone is formed by the os pubis ; it is by means of 

 the union of this bone with its fellow of the opposite side that the pelvic girdle is 

 completed in front. 



The pubis (os pubis) consists of two rami a superior (ramus superior ossis 



