236 



THE SKELETON. 



Fig. 169. Vertical Section of the 

 Pelvis, with lines indicating the Axes 

 of the Pelvis. 



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 transverse. 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 that 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 downwards and forwards; the 

 base of the sacrum in well-formed female 

 bodies being nearly four inches above the up- 

 per border of the symphysis pubis, and the 

 apex of the coccyx a little more than half an 

 inch above its lower border. The obliquity 

 is much greater in the foetus, and at an early 

 period of life, than in the adult. 



Axes of the Pelvis (Fig. 169). 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. 

 A line carried at right angles with this at its middle, 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 extremities 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 the removal of calculi from the bladder, and as determining the direction in 

 which instruments should be used in operations upon the pelvic viscera. 



Differences between the Male and Female Pelvis. In the male the bones are 

 thicker and stronger, and the muscular eminences and impressions on their 

 surfaces more strongly marked. The male pelvis is altogether more massive; 

 its cavity is deeper and narrower, and the obturator foramina of larger size. 

 In the female the bones are lighter and more expanded, the muscular impres- 

 sions on their surfaces are only slightly marked, and the pelvis generally is 

 less massive in structure. The iliac fossae are broad, and the spines of the ilia 

 widely separated; hence the great prominence of the hips. The inlet and the 

 outlet are larger; the cavity is more capacious, and the spines of the ischia 



