238 



OSTEOLOGY. 



female, in whom it is wider and more open. In the female the acetabulum is proportion- 

 ately smaller than in the male. 



The upper opening in the female is large and oval or reniform, as compared with the 

 cribbed and heart-shaped aperture in the male. The sacro-vertebral angle is more pro- 

 nounced in the female, and the obliquity of the upper opening greater. The sacrum is 

 shorter and wider. The posterior superior iliac spines lie wider apart ; the pubic crests 

 are longer; and the pubic tubercles are separated by a greater interval than in man. 

 The outlet is larger ; the tuberosities of the ischia are farther apart ; and the coccyx does 

 not project forward so much. The curve of the sacrum is liable to very great individual 

 variation. As a rule the curve is more uniform in the male, whilst in the female it tends 

 to be natter above and more accentuated below. There is a greater proportionate width 

 between the acetabular hollows in the female than in the male. Of much importance 

 from the standpoint of the obstetrician are the various diameters of the pelvis minor. 

 In regard to this it is worthy of note that the plane of "greatest pelvic expansion" 

 extends from the union between the second and third sacral vertebrae behind, to the 

 middle of the symphysis pubis in front, its lateral boundaries on either side correspond- 

 ing with the mid-point of the medial surface of the acetabulum ; whilst the plane of 

 "least pelvic diameter" lies somewhat lower, and is denned bylines passing through 

 the sacro-coccygeal articulation, the ischial spines, and the lower third of the symphysis 

 pubis (Norris). Subjoined is a table showing the principal average measurements in the 

 two sexes : 



PELVIS MAJOR. 



PELVIS MINOE. 



Growth of the Pelvis. From the close association of the pelvic girdle with the lower limb 

 we find that its growth takes place concurrently with the development of that member. At 

 birth the lower limbs measure but a fourth of the entire body length ; consequently at that time 

 the pelvis, as compared with the head and trunk, is relatively small. At this period of life the 

 bladder in both sexes is in greater part an abdominal organ, whilst in the female the uterus has 

 not yet sunk into the small pelvic cavity, and the ovaries and uterine tubes rest in the iliac 

 fossae. The sacro-vertebral angle, though readily recognised, is as yet but faintly marked. 

 Coincident with the remarkable growth of the lower limbs and the assumption of the erect 

 position when the child begins to walk, striking changes take place in the form and size of tht 

 pelvis. These consist in a greater expansion of the iliac bones, necessarily associated with the 

 growth of the muscles whicn control the movements of the hip, together with a marked increase 

 in the sacro-vertebral angle due to the development of a forward lumbar curve ; at the same time 

 the weight of the trunk being thrown on the sacrum causes the elements of that bone to sinl 

 to a lower level between the hip bones. The cavity of the pelvis minor increases in siz> 

 proportionally, and the viscera afore-mentioned now begin to sink down and have assumed 

 position, within the pelvis by the fifth or sixth year. The extension of the thighs in th 

 upright position necessarily brings about a more pronounced pelvic obliquity, whilst the stoutnes 

 and thickness of the ilium over the upper part of the acetabulum is much increased to withstan 

 the pressure to which it is obviously subjected. Coincident with this is the gradual developmer 



