14(3 THE SKELETON 



diameter, is nunisured from the sacro-vertebral angle to the symphysis. The 

 transverse cHiimeter represents the greatest width of the pelvic cavity. The oblique 

 is measured from tlie saero-ihac synchondrosis to the ilio-pubal ridge. 



The cavity of the true pelvis is l)Ounded in front by the synqjhysis pubis, behind 

 l»y the sacrum and coccyx, and laterally by a smooth wall of bone formed in part 

 1)V the ilium, in part by the ischium; it corresponds to the acetabulum. The cavity 

 is shallow in front, where it is formed l)y the pul)es, and is deepest posteriorly. 



The lower circumference, or outlet, of the pelvis is very irregular, and encroached 

 upon by three bony processes: the posterior process is the coccyx, and the two 

 lateral processes the ischial tuberosities. They separate three notches. The anterior 

 is the pubic arch, and is ))ounded on each side by the conjoined rami of the 

 pubes and ischium. The two remaining gaps correspond to the greater and lesser 

 sciatic notches; they are bounded by the ischium anteriorly, the sacrum and 

 coccyx posteriorly, and the ilium above. These are converted into foramina by 

 the greater and lesser sacro-sciatic ligaments. 



The position of the pelvis. — In the erect position of the skeleton, the plane of 

 the pelvic inlet forms an angle with the horizontal, which varies in individuals from 

 50° to ()0°. The base of the sacrum in an average pelvis lies nearly 10 cm. (4") 

 above the u]iper margin of the symphysis pubis. 



The axis of the pelvis. — This is an imaginary line drawn at right angles to 

 the planes of the brim, cavity, and outlet, through their centres. 



The average measurements of the diameters of the pelvis in the three planes are 

 given below (after Lusk): — 



Diameters At the brim At the outlet 



Conjugate 4^ inches 3f inches 



Transverse 5^ ^' 4^ " 



Oblique 5 " 4J " 



Sexual differences : — 



Male 

 Bones heavier and rougher. 

 Ilia less vertical. 

 Iliac fossae deeper. 

 False pelvis relatively wider. 

 True pelvis deeper. 



" narrower. 

 Inlet more heart-sha])ed. 

 Symphysis deeper. 

 Tuberosities of ischia inflexed. 

 Pubic arch narrower and more pointed. 

 Margins of ischio-pubic rami more 



everted. 

 Obturator foramen oval. 

 Sacruui narrower and n)ore curved. 

 Capacity of true pelvis less. 



Female 

 Bones more slender. 

 Ilia more vertical. 

 Iliac fossise shallower. 

 False pelvis relatively narrower. 

 True pelvis shallower. 



" wider. 

 Inlet more oval. 

 Symphysis shallower. 

 Tuberosities of ischia everted. 

 Pubic arch wider and more rounded. 

 Margins of ischio-i>ubic rami less everted. 



Obturator foramen triangular. 

 Sacrum wider and less curved. 

 Capacity of true pelvis greater. 



