TELYIS. 



157 



the middle, and four inches and a half posteriorly. From this description, it 

 will bo 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 forwards 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-coccygeal 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 pubes 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. 



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

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

 of the symphysis pubis ; and the transverse from the posterior part of one ischiatic 

 tuberosity, to the same point on the opposite side : the average measurement of 

 both is four inches. The antero-posterior diameter varies with the length of the 

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

 this bone. 



Position of the Pelvis. In the erect posture, the pelvis is placed obliquely with 

 regard to the trunk of the body ; the pelvic surface of the symphysis pubis looking 

 upwards and backwards, the concavity of the sacrum and coccyx looking down- 

 wards and forwards; the base of the sacrum, in well-formed female bodies, 

 being nearly four inches above the upper border of the symphysis pubis, and 

 the apex of the coccyx a little more than half an inch above its lower border. 

 This obliquity is much greater in the foetus, and at an early period of life than 

 in the adult. 



Axes of the Pelvis (fig. 102). The plane of the inlet of the true pelvis will be 

 represented by a line drawn from the base of the sacrum to the upper margin of 

 the symphysis pubis. Aline carried 

 at right angles with this, at its middle, Fig. 102. Vertical Section of the Pelvis, with lines 



would correspond at one extremity 

 with the umbilicus, and at the other 

 with the middle of the coccyx ; the 

 axis of the inlet is therefore directed 

 downwards and backwards. The axis 

 of the outlet, produced upwards, would 

 touch the base of the sacrum ; and is 

 therefore directed downwards and 

 forwards. The axis of the cavity is 

 curved like the cavity itself; this 

 curve corresponds to the concavity 

 of the sacrum and coccyx, the ex- 

 tremities being indicated by the 

 central points of the inlet and outlet. 

 A knowledge of the direction of these 

 axes serves to explain the course of 

 the foetus in its passage through the 

 pelvis during parturition. It is also 

 important to the surgeon as indicating 

 the direction of the force required in 



indicating the Axes of the Pelvis. 



