342 



HUMAN ANATOMY 



the ischia, part of the iHa, and the pubic rami and obturator membrane at the sides 

 and front. The plane just described as separating the true and false pelvis is the 

 plane of the inlet^ of the latter. Its greatest individual variations are due to the 

 greater or less projection forward of the sacral promontory. The outlet"^ is bounded 

 behind by the coccyx, from the sides of which the great sacro-sciatic ligaments 

 pass to the ischial tuberosities, thence by the -rami of the ischia and pubes, forming 

 the pubic arch, and by the subpubic ligament below the symphysis. It is evident 

 that these planes converge in front and that the axis of the pelvis (an imaginary line 

 in the centre, perpendicular to an indefinite number of intermediate planes) must be 

 a curved one. 



The Position of the Pelvis. — The plane of the inlet of the pelvis is inclined 

 to the horizon about 60° when the body is upright. This inclination varies accord- 

 ing to the figure and to the individual peculiarities of the pelvis itself. Hermann 

 von Meyer's conjugata vera, a line from the top of the symphysis to the line usually 



Fig. 365. 



Male pelvis from before. 



found in the third sacral vertebra, runs at about 30° with the horizon. This is a more 

 trustworthy angle than that of the plane of the inlet ; but even this is not constant. 

 It is better to try to determine the proper position of every pelvis for itself than to 

 attempt to make all conform to one angle, which for these reasons is impossible. 

 The two borders of the cotyloid notch should be put in the same level, which will 

 bring the anterior superior spines of the ilia into the same vertical plane as the spines 

 of the pubes. The tip of the coccyx should be at about the level of the top of the 

 symphysis ; owing to the many variations of the former, however, its position must 

 be uncertain. The height of the promontory above the symphysis is about 9.5 

 centimetres (3^ inches) in • man and about 10.5 centimetres (4^^ inches) in 

 woman. 



The diameters of the true pelvis of woman are of great practical importance in 

 midwifery. The standards are the antero-posterior, the transverse, and the ob/ique 

 (the latter from the sacro-iliac joint to the acetabulum of the opposite side) measured 

 at the inlet, the outlet, and at an intermediate plane. 



' Apertura pelvis superior. - Apertura pelvis inferior. 



