THE PELVIS. 



433 



Superior view, inlet. 



of the sacrum with its promontory posteriorly. The outlet is formed by the pubic 

 arch anteriorly with the symphysis in the middle, the rami of the pubes and ischia 

 on the sides, and the great sacrosciatic ligaments and coccyx posteriorly. The vis- 

 cera above the inlet are abdominal, those below are pelvic. When the body is 

 vertical the inlet forms an angle of 60 degrees with the horizon, and the promontory 

 of the sacrum is 9 to 10 cm. (3^ to 4 in.) above the upper edge of the symphysis. 



The male pelvis is fashioned preeminently for locomotion: man is the more 

 active, hence the pelvis in the male is both heavier and rougher; the false pelvis 

 is broad and shallow, while the true pelvis is deep and narrow and its capacity is 

 less. The inlet is heart-shaped, the tuberosities closer together, and the pubic arch 

 narrower. The obturator foramen is oval (see Figs. 438 and 439). 



The Female Pelvis. In addition to the functions of the pelvis and its con- 

 tents common to the two sexes the female has the function of child-bearing. To 

 fulfil this function the female pelvis is differ- 

 ent from that of the male. Owing to the 

 less muscular life of the female the pelvis is 

 smoother, its bony prominences not being 

 so marked (see Fig. 440). The extreme 

 width of the pelvis does not differ much 

 in the two sexes, some authorities giving 

 them as of equal size and some stating 

 that the female is slightly narrower. The 

 main difference consists in the modifica- 

 tion of the true pelvis to favor the birth of 

 the child. Its cavity is larger and shal- 

 lower than in the male. The symphysis 

 pubis is shallower and the sacrum is shorter 

 and less curved. The acetabula are set 

 wider apart as are also the tuberosities of 

 the ischia. This causes the thyroid foramen 

 to be triangular in the female while it has 

 a long diameter parallel with the long axis 

 of the body in the male. It also causes 

 the subpubic angle to be greater in the 

 female, forming an angle of about 90 de- 

 grees as against 65 degrees to 70 degrees in 

 the male. The inlet of the female pelvis is 

 more oval and not so heart-shaped as in 

 the male. The cavity is largest at a level 

 between the second and third sacral verte- 

 brae posteriorly and the middle of the sym- 

 physis anteriorly. It is smallest between the sacrococcygeal articulation behind and 

 the lower third of the symphysis in front, and the spines of the ischia on the sides. 

 There are three diameters of the pelvis used in obstetrics; an anteroposterior or conju- 

 gate, an oblique, and a transverse. The size of these varies according to different 

 authors. 



Hirst ("Obstetrics," p. 22), gives the following : 



Anteroposterior 1 1 cm. (4.33 in. ) \ 



Transverse 13-5 cm. (5.3210.) > inlet. 



Oblique 12.75 cm. (5.02 in.) ) 



Anteroposterior n cm. (4.33 in. ) } out i et 



Transverse n cm. (4.33 in.) I 



Dwight, in ' ' Piersol' s Anatomy, ' ' gives them as follows : 



Anteroposterior 



Transverse . . 



Oblique . . . 



28 



Inferior view, outlet. 



FIG. 440. The female pelvis, superior and inferior 

 views, with the diameters of the inlet and outlet. 



