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ATLAS AND TEXT-BOOK OF HUMAN ANATOMY. 



The sacrospinons (lesser sacrosciatic) ligament (Figs. 206, 207, 210, and 211) is more deeph 

 situated than the sacrotuberous ligament, and arises from the lateral margins of the lower portion 

 of the sacrum and of the upper portion of the coccyx. It rapidly becomes narrower and passes 

 almost horizontally forward and outward, crossing the sacrotuberous ligament shortly before 

 reaching its insertion at the tip of the spine of the ischium. Its pelvic surface covers and is 

 adherent to the coccygeus muscle (see Splanchnology). 



The sacrospinous ligament converts the greater sciatic notch into an elliptical foramen which 

 is termed the great sciatic (sacrosciatic) foramen, and the two ligaments, the sacrospinous and 

 the sacrotuberous, convert the lesser sciatic notch into a foramen, the lesser sciatic (sacrosciatic) 

 foramen. This latter foramen is triangular with rounded angles and is separated from the great 

 sciatic foramen by the sacrospinous ligament. The sacrotuberous ligament forms a portion of the 

 outlet of the pelvis. 



THE PELVIS AS A WHOLE. 



The following bones enter into the formation of the pelvis: the two innominate bones, the 

 sacrum, the coccyx, and the fifth lumbar vertebra; and its boundaries are also partly formed by 

 the interpubic fibrocartilage, the obturator membrane, and the sacrotuberous and sacrospinous 

 ligaments. The iliolumbar ligament forms a portion of the pelvic wall. 



In the pelvis may be recognized the false or greater pelvis, and the true or lesser pelvis. The 

 former forms the floor of the abdominal cavity, and is wide open above and in front and is bounded 

 only partly by bone. Its cavity is considerably larger than that of the true pelvis, from which 

 it is separated by the terminal (iliopectineal) line (Fig. 210). It is bounded by the alae of the 

 ilium, by the fifth lumbar vertebra together with the promontory, and by the two iliolumbar liga- 

 ments. 



The true or lesser pelvis is a short canal, the greater portion of whose boundaries are bony. 

 The anterior wall is short while the posterior one is considerably longer, and it is open above and 

 below. The upper opening is termed the superior aperture of the pelvis or the pelvic inlet (Figs. 

 210 and 211), whose boundary is formed by the terminal line, by the promontory, and by the upper 

 margin of the interpubic fibrocartilage. The terminal line is composed of a sacral, an iliac (the 

 arcuate line), and a pubic (crest of the pubis) portion. 



The actual cavity of the pelvis is bounded posteriorly by the concave pelvic surface of the 

 sacrum and by the anterior surface of the coccyx; laterally by the pelvic surfaces of the bodies of 

 the ilium, pubis, and ischium (the floor of the acetabulum), by the sacrotuberous and sacro- 

 spinous ligaments, by the rami of the pubis and ischium, and by the obturator membranes; and 

 anteriorly by the symphysis pubis with its ligaments and by the anterior extremities of the two 

 pubic bones. 



The anterior wall of the pelvic cavity is by far the shortest, while the posterior wall is the 

 longest. The posterior portions of the lateral walls exhibit two openings, the upper elliptical 

 greater sciatic "foramen and the lower triangular lesser sciatic foramen; the anterior portions 

 contain the openings in the obturator membranes which form the obturator canals (seepage 129). 

 The upper more capacious portion of the pelvic cavity is designated as the plane of pelvic 

 expansion, while the inferior contracted portion is known as the plane of pelvic contraction. 



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