chap, xvin.] THE PELVIS. 375 



versely, the two acetalmla tend to be pressed towards 

 one another, the counter arch becomes more bent, 

 and ultimately gives way by indirect violence. The 

 violence continuing, forces the two ilia towards one 

 another, the strain then falls upon the sacro-iliac 

 synchondrosis, and the posterior ligaments of that 

 joint are apt to yield, or portions of the bone adjacent 

 to the joint are torn away. In cases of falls, when 

 the patient alights upon the feet or ischial tuberosities, 

 it can be understood how in many instances the main 

 arches will escape injury owing to their great strength, 

 while the counter arch becomes fractured. Any part 

 of the pelvis, including the sacrum, may be broken 

 by well-localised direct violence. More or less of the 

 iliac crest, the anterior superior and posterior superior 

 spines, have been knocked off. The first-named part 

 may be separated as an epiphysis. It joins the bone 

 at about the twenty-fourth year. In one case the 

 anterior inferior spinous process was torn off by the 

 rectus muscle during the act of running a race. The 

 os innominatum has been broken into its three 

 anatomical portions. This accident cannot take place 

 after about the seventeenth year, since by that time 

 the Y-shaped cartilage is usually fully ossified, and 

 the three elementary bones are firmly united. Before 

 such consolidation occurs abscess in the hip joint not 

 very infrequently makes its way through the cartilage 

 into the pelvis. The acetabulum has been fractured, 

 and the head of the femur driven through its thinnest 

 part into the pelvis. In fractures of the pubes and 

 ischium the bladder has been torn by the sharp 

 fragments. In one case a loose piece of bone that 

 had been driven into the bladder became the nucleus 

 for a stone. The urethra and vagina also have been 

 lacerated, or seriously compressed by the displaced 

 bones. In fractures of the sacrum the rectum has 

 been torn, or has been so compressed by the lower 



