234 OSTEOLOGY. 



inferior surface forms the roof of the broad sulcus obturatorius (obturator groove) 

 which passes obliquely downwards and forwards between the lower margin of 

 the antero-superior surface in front and the inferior sharp border of the posterior or 

 internal surface behind. The inferior ramus of the os pubis passes downwards and 

 laterally from the lower part of the body. Flattened and compressed, it unites with 

 the inferior ramus of the ischium, and thus encloses the obturator foramen, whilst in 

 correspondence with its fellow of the opposite side it completes the formation of 

 the pubic arch. Anteriorly it furnishes origins for the gracilis, adductor brevis, 

 and adductor magnus muscles, as well as some of the fibres of the obturator 

 externus muscle. Its medial surface is smooth, whilst its lower border, rounded 

 or more or less everted, has attached to it the anterior part of the crus penis and 

 the arcuate (O.T. subpubic) ligament. 



The acetabulum is the nearly circular hollow in which the head of the thigh 

 bone fits. As has been already stated, it is formed by the fusion of the ilium and 

 ischium and pubis in the following proportions : the ilium a little less than 

 two-fifths, the ischium somewhat more than two -fifths, the pubis constituting 

 the remaining one-fifth. It is so placed as to be directed downwards, laterally, 

 and forwards, and is surrounded by a prominent margin, to which the capsule and 

 labrum glenoidale of the hip-joint are attached. Opposite the obturator foramen 

 this margin is interrupted by the incisura acetabuli (acetabular notch) ; immediately 

 lateral to the ilio-pectineal eminence the margin is slightly hollowed, whilst 

 occasionally there is a feeble notching of the border above and behind. These 

 irregularities in the outline of the margin correspond to the lines of fusion of the 

 ilium and pubis and the ilium and ischium respectively. The floor of the ace- 

 tabulum is furnished with a horseshoe-shaped articular surface, which lines the 

 circumference of the hollow, except in front, where it is interrupted by the ace- 

 tabular notch. It is broad above; narrower in front and below. Enclosed by 

 articular surface there is a more or less circular rough area (fossa acetabuli) 

 continuous in front and below with the floor of the acetabular notch. This, some- 

 what depressed below the surface of the articular area, lodges a quantity of fat, 

 and provides accommodation for the intra-articular ligament of the joint (ligamentum 

 teres). As may be seen by holding the bone up to the light, the floor of this part of 

 the acetabulum is usually thin. The major part of the non- articular area is 

 formed by the ischium, which also forms the floor of the acetabular notch. 



The foramen obturatum (obturator foramen) lies in front of, below, and 

 medial to the acetabulum. The margins of this opening, which are formed 

 in front and above by the os pubis, and behind and below by the ischium, are 

 sharp and thin, except above, where the antero-inferior surface of the superior ramus 

 of the pubis is channelled by the obturator groove. Below, and on either side of this 

 groove, two tubercles can usually be seen. The one, situated on the edge of the 

 ischium, just in front of the acetabular notch, is named the posterior obturator 

 tubercle ; the other, placed on the lower border of the posterior surface of the 

 superior ramus of the os pubis, is called the anterior obturator tubercle. Between 

 these two tubercles there passes a ligamentous band, which converts the groove 

 into a canal along which the obturator vessels and nerve pass. Elsewhere in the 

 fresh condition the obturator membrane stretches across the opening from margin 

 to margin. The form of the foramen varies much, being oval in some specimens, 

 in others more nearly triangular; its relative width in the female is greater 

 than in the male. 



Nutrient foramina for the ilium are seen on the floor of the iliac fossa, just in front of the 

 auricular surface ; on the pelvic aspect of the bone, close to the greater sciatic notch ; and on 

 the gluteal surface laterally, near the centre of the anterior gluteal line. For the ischium, on its 

 pelvic surface, and also laterally on the groove below the acetabulum. For the pubis, on the 

 surface of the body, and deeply also from the acetabular fossa. 



Connexions. The hip bone articulates with the sacrum behind, with the femur to the 

 lateral side and below, and with its fellow of the opposite side medially and in front. Each 

 of its three parts comes into direct relation with the surface. Above, the iliac crest assists in 

 forming the iliac furrow, which serves to separate the region of the flank from that of the 

 buttock. In front, the anterior superior iliac spine forms a definite landmark ; whilst behind, 

 the posterior superior iliac spines will be found to correspond with dimples situated on 

 either side of the median plane of the root of the back. The symphysis, the crest, and tubercle of 



