THE ISCHIUM 97 



osity continued forward into the ramus. The body has three 

 surfaces, external, internal, and posterior, and three borders. 



The external surface helps form the acetabulum; here it 

 is smooth and concave; below this and above the tuberosity 

 is a horizontal groove for the tendon of the obturator externus 

 muscle. 



The internal surface is roughly quadrilateral, slightly con- 

 cave and smooth, and forms part of the wall of the true pelvis. 

 It is limited above by the ridge marking the junction of the 

 ischium and ilium, in front by the junction with the pubis 

 and by the obturator foramen, and behind by the anterior 

 margin of the great sciatic notch. Below it is continuous with 

 the tuberosity. It gives attachment to a part of the obturator 

 internus muscle. 



The posterior surface is quadrilateral, getting narrow below, 

 and continuous with the tuberosity. It is limited in front by 

 the margin of the acetabulum, behind by the posterior margin 

 of the bone; above it is continuous with the ilium, below with 

 the tuber ischii. Below it presents a part of the groove for 

 the obturator externus, and supports the pyriformis, the two 

 gemelii, and the obturator internus. 



On the posterior border, a little below its middle, is the 

 spine, projecting back and in, and forming the inferior limit 

 of the iliosciatic notch. Internally it gives attachment to the 

 levator ani and coccygeus muscle, and externally to the gemellus 

 superior. The small sciatic notch is between the spine and 

 tuberosity of the ischium. 



The external border is that part of the acetabular rim formed 

 by the ischium. The internal border is thin, and forms the 

 outer boundary of the obturator foramen. 



The tuberosity presents three surfaces external, internal, 

 and posteroinferior. 



The external surface is continuous above with the groove 

 for the tendon of the obturator externus and below with the 

 ramus. In front it is limited by the posterior margin of the 

 obturator foramen, and externally by a prominent margin 

 which separates it from the posteroinferior surface. Close 

 in front of this margin a portion of the quadratus femoris is 

 attached, while in front of it is a part of the obturator externus, 

 and below is the adductor magnus. 



The internal surface is smooth and slightly concave. It 

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