PELVIC BONES . 4t 



smooth, has a sharp well-defined oblique ridge, the ilio-pectineal 

 line, from the auricular surface to the front of the bone. This 

 marks the line of fusion with the pubis, and also divides the 

 true pelvis from the false pelvis. Above the ilio-pectineal line 

 the bone forms the shallow iliac fossa. 



The Ischium consists of a body and two rami superior and 

 inferior. The body forms the inferior and posterior two-fifths 

 of the acetabulum, and from the posterior border of the body 

 projects a sharp spine the ischial spine. From the body the 

 superior ramus passes downwards and back, and from its inferior 

 extremity the inferior ramus passes forwards at an acute angle, 

 to join the inferior ramus of the pubis. The angle of the two 

 ischial rami forms a large tubercle the tuberosity of the 

 ischium and between this and the ischial spine above, the 

 edge of the bone is curved forwards to form the small sciatic 

 notch. 



The Pubis consists of a small triangular body with two rami 

 superior and inferior. The superior ramus completes the re- 

 maining one-fifth of the acetabulum, and the inferior ramus 

 passes backwards to join the inferior ramus of the ischium, thus 

 enclosing the obturator, or thyroid foramen. The upper part of 

 the body projects forwards to form the crest of the pubis, which 

 externally ends in a small spine or tubercle which joins the ilio- 

 pectineal line. The inner border of the body consists of a long,, 

 narrow, oval surface which articulates with its fellow of the 

 opposite side by means of an intermediate disc of cartilage. 



The Acetabulum is practically half a sphere, and is directed 

 downwards and forwards. It has a sharp, well-defined margin, 

 which is interrupted infer iorly, forming the cotyloid notch. 



Ossification. At birth there are three primary centres, one in 

 each bone. Afterwards secondary centres appear for the ischial 

 tuberosity and spine, and inner part of the body of the pubis. 

 The whole bone is usually fused together by the twenty-fifth year. 



The Sacrum, articulating with the innominate bones, completes 

 the pelvis. (For description of sacrum, see the Vertebrae, in. 

 Section IV.) 



The Pelvis is divided into two parts by the ilio-pectineal line, 

 which extends from the sacro-iliac joint behind to the spine of 



