GENERAL REMARKS UPON THE PELVIS. 479 



dry skeleton it is deficient in front, but in the fresh subject 

 it is closed in by the abdominal muscles. The alas of the 

 ilia constitute its lateral and superior boundaries. 



The lower or true pelvis is a perfect bony canal, deeper 

 however, at the sides and behind, than in front; the sacrum 

 and coccyx forming its posterior wall, the ischia and part 

 of the ilia its sides, and the pubis completing it in front. 

 The true pelvis has two orifices, an upper and lower, called 

 the superior and inferior straits, or outlets of the pelvis. 

 The superior strait looks forward and upward, and its axis 

 may be represented by a line drawn from the point of the 

 coccyx to about an inch below the umbilicus. The inferior 

 strait or lower outlet is smaller than the upper, and in the 

 fresh subject is much smaller still, owing to the closing of 

 the sciatic notches, which limits the opening to the space 

 between the arch and rami of the pubis and the coccyx. 

 The opening of the lower strait looks downward and for- 

 ward, and its axis is marked by a line passing through its 

 centre and striking the lower part of the first bone of the 

 sacrum ; so that it will be seen that the perpendiculars to 

 the planes of the two straits have different directions, and 

 decussate or cross each other about the centre of the pelvis, 

 forming an obtuse angle looking forward. The axis of the 

 pelvis describes a curve, the upper strait looking down- 

 ward and backward, the lower strait downward and for- 

 ward, important practical points to recollect in parturition 

 and in the operation for stone. 



DIFFERENCES BETWEEN THE MALE AND FEMALE PELVIS. 



The female pelvis differs from the male in several points. 

 It is larger, the ala3 of the ilia are wider apart, more ex- 

 panded and not so concave ; the depth of the pelvis is not 

 so great. The upper and lower straits are both wider and 

 rounder ; the sacrum is shorter, more concave, and wider ; 

 the promontory of the sacrum is less ; the rami of the pubis 

 are farther apart, but not so long as in the male ; and the 

 arch of the pubis is regularly rounded and smooth, whereas 

 in the male it forms an acute angle. The cartilage at the 



