The pelvic girdle is formed by the sacrum, coccyx, and the two coxae. A coxa is formed by the fusion of three bones, the ilium, ischium, and pubis, which meet in the acetabulum or hip socket. At the back each coxa is attached by strong ligaments to the sacrum (base of spinal cord), and in front to each other at the pubic symphysis joint. This joint allows only slight bending movement, but it softens and becomes more flexible in a female giving birth. [Note: Other names for the pelvic bone are innominate bone and coxal bone.]
|Physical Sex Differences
The following sex differences are true for the hypothetical "average" male and female.
Genitals and Functions
Males have penises and testes; females have vaginas and wombs.
Males and females differ in form. Their curves and angles. or their shapes are different, generally and relatively. Females generally have a more roundish look because their subcutaneous fat covers and hides their muscles. Men do not have women's characteristic layers of fat beneath their skin, and therefore their appearance is more roughish because their muscle tissues show through their skin more so than females.
Women's eyes are set further apart than men's. Women's eye brow is lighter than men's in appearance. Looking toward the front, women's face is rounder, broader than men's. Looking from the top down on the head, women's head is rounder, while men's head is longer from front to back.
Breasts and Shoulders
Women have developed breasts with larger nipples and areolas than men. Women's shoulders are more narrow, rounded, and sloping than men's.
Angle of Arms and Legs
The angle of women's thigh and lower leg gives a "knock-knee" effect to females, while men's form a straight line. Also women's arms form a bent "carrying angle" at the elbow, while men's "carrying angle" is straight.
Hips and Legs
Looking towards the front, women's hips are wider than men's, and their hips have a more round'ish curve than men's. Women's legs have a conical shape, while men's legs have a cylindrical look.
Hands and Feet
Women's hands and feet are relatively smaller, narrower, and more delicate looking than men's.
Women do not have noticeable hair like men on their chest, arms, legs and other bodily areas. Women's pubic hair is formed like a triangle pointing down; men's pubic hair forms a triangle pointing up. Women do not loose head hair like many men do in old age.
Women are generally smaller and more delicate than men. The following apply generally for those of western European descent:
By age 20 years, women are generally 10 percent shorter than men.
By age 20, women are generally 20 percent lighter than men.
Adult men are generally 50 to 60 percent stronger than women.
Factors contributing to the overall shape of the pelvis are constrained by both the demands of bipedal locomotion, as well as those for perpetuating the species. Of all the bones, the pelvis shows the greatest sexual differentiation, principally in relation to the requirements of childbirth. On average the male pelvis is much heavier and narrower than that of the female. In comparison the female pelvis is broad and shallow, the geometry is designed with a greater outlet for passage through its bony openings of a baby's head and shoulders during birth. The female pelvis is also less massive and more delicate and its muscular impressions are slightly marked.
In the female pelvis the ilia are less sloped, and the anterior iliac spines more widely separated; hence the greater lateral prominence of the hips. The pelvic inlet of females is larger and has a greater absolute circumference. The body of the pubis is longer, thereby increasing the size of the pelvic outlet. The size of the pelvis varies not only in the two sexes, but also in different members of the same sex, and does not appear to be influenced in any way by the height of the individual. Women of short stature, as a rule, have broad pelvises. The characteristic differences between the male and female pelvis are distinctly indicated as early as the fourth month of fetal life.
In the female, the superior ramus of the pubic bone is longer, increasing the pubic/ischium ratio. The greater sciatic notch is wider and forms a longer angle. The increased pubic length and laterally displaced ischia result in a wider subpubic angle. The growth and remodelling of the pubis produces extra bone at the symphysis, leaving a concave inferior ramus, a ventral arc that represents a previous border of the symphysis, and a narrow inferior pubic ramus. The female pubic symphysis is likely to be longer in its superior-inferior diameter and smaller in its dorsal-ventral diameters than is that of a male. Females are more likely to have a well-developed preauricular sulcus, and those who have borne children may have pits or guttering along the dorsal border of the pubic symphysis. Since they have smaller femurs, females have smaller acetabula, with males showing greater robusticity in this feature corresponding to the generally greater size of the male femur head with which it articulates.
The greater sciatic notch is an often-used preliminary tool for sex determination, though not the most accurate.
A triangular shaped pubis with a broad medial aspect and no evidence of a ventral arc is a characteristically male pattern. The female pattern for these features is a rectangular pubis, pronounced ventral arc, and sharp, narrow medial aspect of the ischiopubic ramus. According to Bass, the presence of a ventral arc is the most diagnostic of the female pubic features.
As a rule, the female sacrum is wider and flatter than that of the male, permitting a greater outlet for the birth canal. However, this is a rather subjective observation, and should only be used in conjunction with other techniques of sex determination.
(Sacral index = sacral anterior breadth X 100/divided by sacral anterior height)
Comparison of the Males and Female Pelvises:
||More massive; rougher; heavier
||Less massive; smoother; more delicate|
||Upper end of pelvis relatively vertical
||Upper end of pelvis tilted forward|
||Deeper; projects further above sacroiliac joint
||Shallower; does not project as far above sacroiliac joint|
||Narrower and longer with pronounced sacral curvature
||Shorter and wider with less curvature|
||Less movable; more vertical
||More movable; tilted backward|
|Width of greater pelvis
||Anterior superior spines closer together; hips less flared
||Anterior superior spines further apart; hips more flare|
||heart shaped, less space
||oval to round shape, spacious|
||Shorter; smooth, moveable|
|Greater sciatic notch
||large, oval shaped
||small, triangular shaped|
||Faces more laterally; larger
||Faces slightly anteriorly; smaller|
||Subpubic angle usually less than 90 degrees (narrow)
||greater than 100 degrees (wide)|
||no ventral arc
|Ischiopubic ramus (ramus of ischium)
||broad on the medial aspect
||narrow on the medial aspect|
|Preauricular sulcus (depression between sciatic notch and sacroiliac articulation)
Sexual Dimorphism in the Human Pelvis
(Note the minimal overlap between the male and female ranges,
indicating that relatively few pelvises are ambiguously male or female)
(Source: Schultz 1949 and A & D 1990)
The following diagrams compares the male and female pelvis, notice the differences in the pelvises shown below, especially the much wider pubic arch and birth canal (aka pelvic outlet/inlet) in the female. Also, the ischia spines are less pronounced and significantly further apart in a female - in order to allow the the head of a baby to pass through.