THE PELVIS. 281 



the plane. It is smaller than the false pelvis, but its walls are more perfect. For 

 convenience of description it is divided into a superior circumference or inlet, an 

 inferior circumference or outlet, and a cavity. 



The superior circumference forms the margin or brim of the pelvis, the included 

 space being called the inlet. It is formed by the linea ilio-pectinea. completed in front 

 by the crests of the pubic bones, and behind by the anterior margin of the base of 

 the sacrum and sacro-vertebral angle. The inlet of the pelvis is somewhat heart- 

 shaped obtusely pointed in front, diverging on either side, and encroached upon 

 behind by the projection forward of the promontory of the sacrum. It has three 

 principal diameters : antero-posterior (sacro-pubic). transverse, and oblique. The 

 antero-posterior extends from the sacro-vertebral angle to the symphysis pubis ; 

 its average measurement is four inches in the male, fojir and three-quarters in the 

 female. The transverse extends across the greatest width of the inlet, from the 

 middle of the brim on one side to the same point on the opposite: its average 

 measurement is four and a half in the male, five and a quarter in the female. 

 The oblique extends from the margin of the pelvis, corresponding to the ilio- 

 pectineal eminence on one side, to the sacro-iliac symphysis on the opposite 

 side: its average measurement is four and a quarter in the male, and five in 

 the female. 



The cavity of the true pelvis is bounded in front by the symphysis pubis ; 

 behind, by the concavity of the sacrum and coccyx, which, curving forward above 

 and below, contracts the inlet and outlet of the canal : and laterally it is bounded 

 by a broad, smooth, quadrangular surface of bone, corresponding to the inner 

 surface of the body of the ischium and that part of the ilium which is below 

 the ilio-pectineal line. The cavity is shallow in front, measuring at the symphy- 

 sis an inch and a half in depth, three inches and a half in the middle, and four 

 inches and a half posteriorly. From this description it will be seen that the 

 cavity of the pelvis is a short, curved canal, considerably "deeper on its posterior 

 than on its anterior wall, and broader in the middle than at either extremity, from 

 the projection forward of the sacro-coccygeal column above and below. This 

 cavity contains, in the recent subject, the rectum, bladder, and part of the organs 

 of generation. The rectum is placed at the back of the pelvis, and corresponds to 

 the curve of the sacro-cocc-ygeal column ; the bladder in front, behind the symphysis 

 pubis. In the female the uterus' and vagina occupy the interval between these 

 parts. 



The lower circumference of the pelvis is very irregular, and forms what is 

 called the outlet. It is bounded by three prominent eminences : one posterior, 

 formed -by the point of the coccyx : and one on each side, the tuberosities of the 

 ischia. These eminences are separated by three notches; one in front, the pubic arch, 

 formed by the convergence of the rami of the ischia and pubic bones on each side. 

 The other notches, one on each side, are formed by the sacrum and coccyx behind, 

 the ischium in front, and the ilium above : they are called the sacro-sciatic notches ; 

 in the natural state they are converted into foramina by the lesser and greater 

 sacro-sciatic ligaments. In the recent state, when the ligaments are in situ, the 

 outlet of the pelvis is lozenge-shaped, bounded in front by the subpubic liga- 

 ment and the rami of the os pubis and ischium : on each side by the tuberosities 

 of the ischia ; and behind by the great sacro-sciatic ligaments and the tip of the 

 coccyx. 



The diameters of the outlet of the pelvis are two, antero-posterior and trans- 

 verse. The antero-potterior extends from the tip of the coccyx to the lower part 

 of the symphysis pubis : its average measurement is three and a quarter inches in 

 the male and five in the female. The antero-posterior diameter varies with the 

 length of the coccyx, and is capable of increase or diminution on account of the 

 mobility of that bone. 1 The franzi'i 'fte extends from the posterior part of one 



1 The measurements of the pelvis given above are, I believe, fairly accurate, but different meas- 

 urements are given by various authors, no doubt due in a great measure to differences in the phys- 

 ique and stature of the population from whom the measurements have been taken. The accompany- 



