The hipbones are called in Latin the ossa innominata (nameless bones) and each hipbone is composed of three bones: the ilium, the ischium, and the os pubis. The thighs are attached to the hipbones, and to the hipbones are also attached the large _gluteal_ muscles, which form the buttocks, or the "seat." The pelvis of the female differs considerably from the pelvis of the male. The female pelvis is shallower and wider, less massive, the margins of the bones are more widely separated, thus giving greater prominence to the hips; the sacrum is shorter and less curved, and the pubic arch is wider and more rounded. All this is necessary in order to permit the child's head to pass through. If the female pelvis were exactly like the male pelvis, a full-term living child could never pass through it. The two illustrations show the differences between the male and female pelvis very clearly. Note particularly the differences in the pubic arches: in the male pelvis it is really more of an angle than an arch. Also note how much longer and more solid the sacrum (with its attached bone, called the coccyx[2]) is in the male pelvis. The differences in the pelves (the plural of pelvis is pelves) of the male and female become fully marked at puberty, but they are present as early as the fourth month of intra-uterine life. FOOTNOTES: [1] Mucous membrane--briefly a membrane which secretes mucus or some other fluid. [2] The coccyx consists of three rudimentary vertebrae; it is the vestige of an organ which we once possessed in common with many other animals, namely--a tail. CHAPTER THREE THE PHYSIOLOGY OF THE FEMALE SEX ORGANS Function of the Ovaries--Internal Secretion of the Ovaries--Function of the Internal Secretion--Number of Ova in the Ovaries--The Graafian Follicles--Ovulation--Corpora Lutea--Function of the Fallopian Tubes--Function of the Vagina--Functions of the Vulva, Clitoris and Mons Veneris--Function of the Breasts--Besides Secreting Milk Breast Has Sexual Function--The Orgasm--Pollutions in Women--Secondary Sex Characters--Differences Between Woman and Man. The importance of an organ depends upon its _function_, upon what it does, and not so much upon what it is. It is important to know the size, structure and location of an organ, but it is still more important to know its function; in other words, for our purpose it is more important to know the _physiology_ than the anatomy of the sex organs. SUBCHAPTER A FUNCTION OF THE OVARIES