348 HUMAN ANATOMY. 



The anterior inferior spine, wliich is peculiar to the human pelvis, and affords 

 a slight leverage which partly enables the rectus femoris to overcome the disadvan- 

 tage of the erect position, has been torn off in the act of running. 



Although the ischial tuberosities are subjected to enormous pull from the pow- 

 erful hamstring muscles, as in the act of suddenly straightening the trunk from a 

 bending position (when these bones project far behind the axial plane and thus offer 

 better leverage), their epiphyseal disjunction or their fracture from muscular action 

 is practically unknown. From direct violence both of these lesions occur, but with 

 great rarity. 



3. Considered in relation to the abdominal and thoracic viscera, the injuries 

 and diseases of the bones of the pelvis are of great importance. Fractures of the 

 false pelvis have been followed by fatal wound of the small intestine. Fractures 

 running through the brim of the pelvis have been associated with hemorrhage from 

 the iliac vessels ; fractures of the pubis and ischium have constantly been compli- 

 cated by wounds of the urethra and bladder, and even of the rectum. The- pos- 

 sibility of these complications should never be forgotten. The obvious ana- 

 tomical reasons for their occurrence will be recurred to when these viscera are 

 described. 



Disease of the pelvic bones, like their deformities, is of chief importance in its 

 relation to parturition. 



In rickets the shape of the pelvis is modified through the medium of the super- 

 imposed weight of the trunk and through the pull of muscles resisted by the inter- 

 osseous ligaments. 



The weight of the body, aided by the psoas muscles, tends to press the sacrum 

 downward and forward between the iliac bones and to rotate the upper end forward 

 on a transverse axis. The sacro-sciatic and sacro-iliac ligaments resist this force, 

 which thus results in thrusting the promontory of the sacrum towards the pubes and 

 in increasing the sacro-vertebral angle, or making a sharp bend in it, often at the 

 junction of the fourth and fifth sacral vertebrae. The sacro-iliac ligaments convey 

 this movement to the posterior superior spinous processes, which, advancing some- 

 what forward and inward, would tend to throw the anterior half of the innominate 

 bones outward. These are held, however, firmly at the symphysis and — much less 

 effectively — by Poupart's ligament. The ilia are thus thrown outward and back- 

 ward, so that the distance between their spines may be equal to or greater than 

 that between the summits of the crests. As a further result of these combined 

 forces pushing the innominate bones forward from behind and holding them in place 

 in front, they are abnormally curved, as a bow is bent between one's hand and the 

 ground (Hirst). This bending of the ilia, together with the pull of the external 

 rotators of the thigh (increased by the usual bowing of the femurs), carries the 

 tuberosities of the ischium outward, so that they diverge like a monkey's, flattening 

 and widening the pubic arch and increasing the transverse dmmeter. The weight of 

 the trunk on the summit of the sacrum is so much the most effective and continuous 

 force applied as the growing child walks or stands that the whole pelvis is tilted 

 forward on its transverse axis, the inclination of the superior strait being increased 

 and the external genitals displaced backward. 



In osteomalacia the bones are much softer than in rickets and the mechanism 

 of the pelvic deformity is simpler. The sacrum yields under the pressure of the 

 body weight, and becomes acutely angulated and driven forward and downward into 

 the pelvis ; the ischia and pubes are pushed inward and backward by the force 

 transmitted through the acetabula, the pubic angle is greatly increased, and the 

 pelvis assumes an irregularly triangular or " triradiate" shape. 



The rhachitic and osteomalacic pelves may approximate each other in shape, but 

 are usually distinct. 



Exostoses of the pelvis are usually found over one of the joints, or at points of 

 muscular or fascial attachment, as along the pubic crests where the iliac fascia is 

 inserted. 



Enchondroma is relatively common in the pelvis, and other growths occasion- 

 ally originate there. 



Congenital tumors are often found in the sacro-coccygeal region. Their shape 



