234 THE SKELETON. .*_ , 



through the intervention of this Y-shaped portion. At about the age of pu- 

 berty, ossification takes place in each of the remaining portions, and they be- 

 come joined to the rest of the bone about the twenty-fifth year. 



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



Attachment of Muscles. Ilium. To the outer lip of the crest, the Tensor 

 Vaginae Femoris, Obliquus Bxternus Abdominis, and Latissimus Dorsi ; to the 

 internal lip, the Transversalis, Quadratus Lumborum, and Erector Spinse ; 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 Rectus, portion of Pyriformis; to the internal surface, the Iliacus; to 

 the anterior border, the Sartorius and straight tendon of the Eectus. Ischium, 

 To its outer surface, the Obturator Externus ; internal surface, Obturator In- 

 ternus, and Levator Ani. To the spine, the Gemellus Superior, Levator Ani, 

 and Coccygeus. To the tuberosity, the Biceps, Semi-tendinosus, Semi-mem- 

 branosus, Quadratus Femoris, Adductor Magnus, Gemellus Inferior, Transversus 

 Perinei, Erector Penis. Pubes. The Obliquus Externus, Oliquus Internus, 

 Transversalis, Rectus, Pyramidalis, Psoas Parvus, Pectineus, Adductor Longus, 

 Adductor Brevis, Gracilis, Obturator Externus and Internus, Levator Ani, 

 Compressor Urethra, and occasionally a few fibres of the Accelerator Urinae. 



THE PELVIS (Figs. 167; 168). 



The Pelvis, so called from its resemblance to a basin, 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 spine, 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 a prominent line, the linea ilio-pectinea, into the 

 false and true pelvis. 



The False Pelvis is all that expanded portion of the pelvic cavity which is 

 situated above the linea ilio-pectinea. 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. 



The True Pelvis is all that part of the pelvic cavity which is situated beneath 

 the linea ilio-pectinea. 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 forms the margin or brim of the pelvis, the included 

 space being called the inlet. It is formed by the linea ilio-pectinea, completed 

 in front by the spine and crest of the pubes, and behind by the anterior margin 

 of the base of the sacrum and sacro-vertebral 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 forwards 

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

 posterior (sacro-pubic), transverse, and oblique. The antero-posterior extends 

 from the sacro-vertebral angle to the symphysis pubis; its average measurement 

 is four inches. The transverse extends across the greatest width of the inlet, 

 from the middle of the brim on one side to the same point on the opposite; its 

 average measurement is five inches. The oblique extends from the margin of 

 the pelvis, corresponding to the ilio-pectineal eminence on one side, to the sacro- 

 iliac symphysis on the opposite side; its average measurement is also five inches. 



The cavity of the true pelvis is bounded in front by the symphysis pubis ; 

 behind by the concavity of the sacrum and coccyx, which, curving forwards 



