374 SVRC.ICAL APPLIED ANATOMY. [Chap. xvni. 



collapse, and the horizontal rami of the pubes be for 

 some little way parallel to one another. 



In the erect attitude the pelvis is so inclined that 

 the plane of the brim of the true pelvis forms with 

 the horizon an angle of from 60 to 65 ; the base of 

 the sacrum is about 3|- inches above the upper border 

 of the symphysis, while the tip of the coccyx is a little 

 higher than its lower border. The centre of gravity 

 of the whole body (adult) is at a spot just ubuve the 

 sacro-lumbar angle, and exactly over the mid-point of 

 a line drawn between the heads of the femora. The 

 obliquity of the pelvis materially assists in breaking 

 shocks, and in distributing forces applied from below 

 throughout the pelvic ring. In modifying the effect 

 of shocks, also, it is aided by the arches of the pelvis, 

 and by the buffer-like discs of cartilage at the 

 symphysis and sacro-iliac joints. 



Fractures of the pelvis. From what has 

 been already said, it may be surmised that the weakest 

 parts of the pelvis are at the symphysis and the sacro- 

 iliac joints. The bones of these parts, however, are 

 so very firmly knit together by powerful ligaments 

 that it is very rare for these articulations to give way, 

 fracture of the adjacent bones being more common. 

 The commonest fracture of the pelvis is in the weak 

 counter arch, and involves the rami of both the pubes 

 and the ischiuni. The fracture is often associated with 

 some tearing of ligaments about the sacro-iliac synchon- 

 drosis, and is met with in accidents due to the most 

 varied forms of violence. This last remarkable circum- 

 stance is thus explained by Tillaux. If the pelvis be 

 compressed in (a) an antero-posterior direction, the 

 main brunt of the force comes upon the weak counter 

 arch, which fractures from direct violence. The force 

 continuing, tends to push asunder the two iliac bones, 

 and so causes rupture of the anterior ligaments at the 

 sacro-iliac joint. If the force be applied (6) trans- 



