THE OS INNOMINATUM. 127 



spinous processes, superior and inferior, separated by the 

 superior notch ; below the inferior spine is the inferior 

 notch. The spinous processes are about one and one- 

 half to two inches apart ; they serve for muscular attach- 

 ment. The posterior border presents the superior and 

 inferior spines, separated by a notch; below the inferior 

 spine is a deep notch, called the greater sacro-sciatic. 

 The posterior inferior spine is prominent and strong, and 

 gives attachment to ligaments. 



The pubic portion of the os innominatum makes the 

 anterior part of the pelvis ; it presents a body and de- 

 scending ramus. The body presents four surfaces su- 

 perior, inferior, anterior, and posterior and an inner 

 and outer extremity. The anterior surface is rough, for 

 the attachment of muscles; the posterior surface is 

 smooth and makes the upper part of the anterior wall 

 of the pelvis; the superior surface presents, about three- 

 fourths of an inch from the inner extremity, a conical 

 elevation of bone, called the spine. Running inward 

 from the spine is the crest for attachment of the rectus 

 muscle. Passing outward from the spine is the begin- 

 ning of the ilio-pectineal line, which runs outward and 

 backward, becoming strongly marked ; it limits the venter 

 of the ilium, and, in the articulated pelvis, divides the 

 upper, or false, from the lower, or true, pelvis. The in- 

 ferior surface is smooth, and forms part of the upper 

 boundary of the obturator foramen and presents a shal- 

 low groove for the passage of the obturator nerve and 

 vessels. The inner extremity presents an oval surface; 

 its long diameter is directed vertically; it is roughened, 

 and affords attachment to the interarticular fibro-carti- 

 lage, interposed between the two pubic bones. 



Passing downward and outward from the inner ex- 

 tremity of the body is the descending ramus. The outer 



