490 



APPLIED ANATOMY. 



THE BONY PELVIS. 



The pelvis is composed of the pelvic girdle on each side (innominate bones), 

 and the sacrum and coccyx posteriorly. It serves two purposes. It supports and 

 protects the abdominal and pelvic viscera, and serves as the connection between the 

 trunk and the lower limb. It is divided into two parts the false pelvis, above the 

 iliopectineal line, and the true pelvis, below the iliopectineal line. 



The false pelvis serves to support the abdominal viscera, as its name indicates, 

 like a basin. In man it is large and flaring because his normal position is upright, 

 but in the lower animals, as the quadrupeds, whose normal position is horizontal, it 

 is smaller and less prominent. 



The true pelvis contains and protects . the pelvic organs and also serves as the 

 connecting link between the trunk above and the extremity below; hence, as it has 

 a double function, it has of necessity a composite structure. In order to contain and 

 protect the pelvic viscera it is made hollow, and in order to support the weight of 

 the body on the legs it is made strong. The pelvic contents are not exposed to 

 injury to the same extent as is the brain; therefore, instead of having a complete 

 covering of bone, like the skull, the bony pelvis is merely a framework comprised 

 solely of those parts essential to strength. 



The pelvis supports the trunk in two postures, the standing and sitting. In the 

 former the weight is transmitted through the acetabula, and in the latter to the 

 tuberosities of the ischia. 



MECHANISM OF THE PELVIS. 



As was pointed out by Henry Morris ("The Anatomy of the Joints of Man," 

 p. 115), the bony pelvis is composed of arches. The two main arches are the 

 femorosacral and the ischiosacral. These are strengthened by subsidiary arches 

 which join the extremities of the main arches so as to strengthen and fix them. 



I 



FIG. 491. The femorosacral arch. The main arch 

 passes upward from one hip-joint to the other through 

 the sacrum : the subsidiary arch passes downward from one 

 hip-joint to the other through the pubes. 



FIG. 492. The ischiosacral arch. The main arch 

 passes upward from one tuberosity of the ischium 

 through the sacrum down to the opposite tuberosity; 

 the subsidiary arch passes forward from one tuber- 

 osity of the ischium through the pubes and back to the 

 opposite tuberosity. 



Femorosacral Arch. This arch extends from the acetabula on the sides to 

 the sacrum in the middle, which is its keystone. The weight of the body is trans- 

 mitted downward through the spine to the sacrum, and then through the two sides 

 of the femorosacral arch to the heads of the femurs. For an arch to be effective its 

 two extremities must be firmly anchored, so that they do not separate when pressure 

 is made on it. In artificial arches, as used in bridges, this separation is guarded 

 against by a rod running from one extremity to the other, forming a chord of the 

 In the pelvis this mechanism is impossible, because this " tie-rod" would 



arc. 



