THE PELVIS 215 



intervention of this Y-shaped portion. At about the age of puberty ossification, takes place 

 in each of the remaining portions, and they become joined to the rest of the bone between the 

 twentieth and twenty-fifth years. Separate centres are frequently found for the pubic and ischial 

 spines. 



Articulations. With its fellow of the opposite ^ide, the sacrum, and femur. 



Attachment of Muscles. To the ilium, sixteen. To the outer lip of the crest, the Tensor 

 vaginae femoris, Obliquus externus abdominis, and Latissimus dorsi; to the internal lip, the 

 Iliacus, Transversalis, Quadratus lumborum, and Erector spinae; to the interspace between the 

 lips, the Obliquus internus. To the outer surface of the ilium, the Gluteus maximus, Gluteus 

 medius, Gluteus minimus, reflected tendon of the Rectus femoris; to the upper part of the great 

 sacrosciatic notch, a portion of the Pyriformis; to the internal surface, the Iliacus; to that portion 

 of the internal surface below the iliopectineal line, the Obturator internus to the internal surface 

 of the posterior superior spine, and the Multifidus spinae; to the anterior border, the Sartorius 

 and straight tendon of the Rectus femoris. To the ischium, thirteen. To the outer surface of 

 the ramus, the Obturator externus and Adductor magnus; to the internal surface, the Obturator 

 internus and Erector penis. To the spine, the Gemellus superior, Levator ani, and Coccygeus. 

 To the tuberosity, the Biceps, Semitendinosus, Semimembranosus, Quadratus femoris, Adductor 

 magnus, Gemellus inferior, Transversus perinei, Erector penis. To the pubis, sixteen: Obliquus 

 externus, Obliquus internus, Transversalis, Rectus abdominis, Pyramidalis, Psoas parvus, 

 Pectineus, Adductor magnus, Adductor longus, Adductor brevis, Gracilis, Obturator externus 

 and internus, Levator ani, Compressor urethrae, and occasionally a few fibres of the Accelerator 

 urinae. 



THE PELVIS (Figs. 170, 171). 



The pelvis is stronger and more massively constructed than either the cranial 

 or thoracic cavity; it is a bony ring, interposed between the lower end of the verte- 

 bral column, which it supports, and the lower extremities, upon which it rests. 

 It is composed of four bones the two ossa innominata, which bound it on either 

 side and in front, and the sacrum and coccyx, which complete it behind. The 

 pelvis is divided by an oblique plane passing through the prominence of the 

 sacrum, the iliopectineal line, and the upper margin of the symphysis pubis 

 into the false and true pelvis. 



The False Pelvis (pelvis major} is the expanded portion of the pelvic cavity 

 which is situated above this plane. It is bounded on each side by the ossa ilii; 

 in front it is incomplete, presenting a wide interval between the spinous processes 

 of the ilia on either side, which is filled up in the recent state by the parietes of 

 the abdomen; behind, in the middle line, is a deep notch. This broad, shallow 

 cavity is fitted to support the intestines and to transmit part of their weight to 

 the anterior wall of the abdomen, and is, in fact, really a portion of the abdominal 

 cavity. The term false pelvis is incorrect, and this space ought more properly to 

 be regarded as part of the hypogastric and iliac regions of the abdomen. 



The True Pelvis (pelvis minor} is that part of the pelvic cavity which is 

 situated below the iliopectineal line. It is smaller than the false pelvis, but its 

 walls are more perfect. For convenience of description it is divided into a superior 

 circumference, or inlet, an inferior circumference, or outlet, and a cavity. 



The superior circumference, or inlet (apertura pelvis superior}, forms the brim 

 of the pelvis, the included space being called the inlet. It is formed by the ilio- 

 pectineal line, completed in front by the crests of the pubic bones, and behind 

 by the anterior margin of the base of the sacrum and sacrovertebral angle. The 

 inlet of the pelvis is somewhat heart-shaped, obtusely pointed in front, diverging 

 on either side, and encroached upon behind by the projection forward of the 

 promontory of the sacrum. It has three principal diameters antero-posterior 

 (sacropubic), transverse, and oblique. The antero-posterior or conjugate diameter 

 (conjugata} extends from the sacrovertebral angle to the symphysis pubis. Its 

 average measurement is four inches in the male and four and three-fifths inches 

 in the female. The transverse diameter (diameter transversa) extends across 

 the greatest w r idth of the inlet, from the middle of the brim on one side to the 



