216 OSTEOLOGY. : 
posterior inferior iliac spine is longer, measuring on an average 50 mm. (2 inches) in the 
female, as contrasted with 40 mm. (12 inches) in the male. 
The inlet 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 pronounced in the 
female, and the obliquity of the inlet greater. The sacrum is shorter and wider. The 
posterior superior iliac spines lie wider apart ; the pubic crests are longer ; and the pubic 
spines are separated by a greater interval than in man. ‘The outlet is larger; the tubero- 
sities of the ischia are far 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 flatter 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 true pelvis. 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 vertebree behind, to the middle of the symphysis pubis in front, 
its lateral boundaries on either side corresponding with the mid-point of the inner surface 
of the acetabulum ; whilst the plane of “least pelvic diameter” lies somewhat lower, and 
is defined by lines 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 :— 
| Males. Females. 
Maximum distance between the iliac crests . | 114 in, or 282 mm. 102 in., or 273 mm. 
ry vs . . a 8. ? 4. ? 
Distance between the anterior superior iliac | 94 in., or 240 mm. 931n., or 250 mm. | 
spines | 
Distance between the last lumbar spine and | 7 in., or 176 mm. 74 in., or 180 mm. 
the front of the symphysis pubis | 
TRUE PELVIS. 
MALEs. FEMALES. 
Cavity. 
Inlet. Outlet. Inlet. - -| Outlet. 
Greatest. Least. 
= | 7 a : | 
Antero-posterior (conju-|4 in, or|32 in. or/4% in, or|5 in, or/4% in, or|4$ in, or} 
gate) diameter | 1Olmm.| 95 mm. 110 mm.}| 127mm.} 110mm.} 115 mm. | 
Oblique diameter . .|42 in. or|/3$ im, or/5 in, or te | cs 44 in., or | 
| a i! 
| 120mm.| 88 mm. 125 mm. 115 mm. 
Transverse diameter ./5 in, or|34 im, or|5} in, or;4% in, or|/43 im, or|4% im, or} 
127 mm.} 88 mm. 135 mm.; 125mm./ 110mm.| 110 mm. | 
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 true pelvic cavity, and the ovaries and Fallopian tubes rest in the iliac 
fosse. 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 the 
pelvis. These consist in a greater expansion of the iliac bones necessarily associated with the 
growth of the muscles which 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 sink to 
a lower level between the innominate bones. The cavity of the true pelvis increases in size 
proportionally, and the viscera afore-mentioned now begin to sink down and have assumed a 
position within the pelvis by the fifth or sixth year. The extension of the thighs in the 
upright position necessarily brings about a more pronounced pelvic obliquity, whilst the stoutness 
and thickness of the ilium over the upper part of the acetabulum is much increased to withstand 
the pressure to which it is obviously subjected. Coincident with this is the gradual development 
