98 OSTEOLOGY, OR ANATOMY OF OSSEOUS SYSTEM 



is limited in front by the margin of the obturator foramen; 

 behind and below by a sharp ridge for the attachment of the 

 falciform prolongation of the great sciatic ligament. 



The poster oinferior surface of the tuberosity presents two 

 lips and an intermediate space. The external lip gives attach- 

 ment to the quadra tus femoris and adductor magnus; the 

 inner lip to the falciform portion of the great sacrosciatic 

 ligament. The intermediate space is divided into two por- 

 tions ; the anterior part attaches the adductor magnus externally 

 and the great sacrosciatic ligament internally; the posterior 

 part has two facets, an upper and outer for the semimembra- 

 nosus, a lower and inner for the biceps and semitendinosus. 



The ramus joins the descending ramus of the pubis at the 

 inner side of the .thyroid foramen. Its outer surface is rough, 

 and gives attachment to the obturator externus, adductor 

 magnus, and gracilis. The crus penis and transversus peronei 

 are attached to the inner border. 



The acetabulum, or cotyloid cavity, is cup-shaped, and looks 

 out, down, and forward. It is formed by portions of the ilium, 

 pubis, and ischium. Scant two-fifths is ilium, a little more 

 than two-fifths is ischium, and a little more than one-fifth pubis. 

 It is nearly surrounded by a prominent rim which presents 

 three depressions a slight one anteriorly and posteriorly, 

 and the cotyloid notch below. In the lateral and upper parts 

 of the cavity is a broad horseshoe-shaped articular surface. 



The central part of the cup and the notch are depressed 

 (fossa acetabuli), and contain fat and the interarticular liga- 

 ment (ligamentum teres or round ligament). This non-articular 

 surface belongs mostly to the ischium. 



The thyroid or obturator foramen (foramen ovale) is internal 

 to and below the acetabulum. It is nearly oval in the male, 

 more triangular in the female. It is closed by fibrous mem- 

 branes, except in the region of the obturator groove in its upper 

 margin. 



The Pelvis as a Whole 



The pelvis (basin) is composed of four boiies: two ossa 

 innominata, the sacrum, and coccyx. It is divided into two 

 parts by a plane passing through the sacral promontory, ilio- 

 pectineal lines, and upper border of the symphysis. This 

 circle is the inlet or brim of the true pelvis; the space above it 



