As Ploss and Bartels remark, a very common variation among European women consists in an unusually posterior position of the vulva and vaginal entrance, so that unless a cushion is placed under the buttocks it is difficult for the man to effect coitus in the usual position without giving much pain to the woman. They add that another anomaly, less easy to remedy, consists in an abnormally anterior position of the vaginal entrance close beneath the pelvic bone, so that, although intromission is easy, the spasmodic contraction of the vagina at the culmination of orgasm presses the penis against the bone and causes intolerable pain to the man. The mons veneris and the labia majora are, after the age of puberty, always normally covered by a more or less profuse growth of hair. It is notable that the apes, notwithstanding their general tendency to hairiness, show no such special development of hair in this region. We thus see that all the external and more conspicuous portions of the sexual sphere in woman--the mons veneris, the labia majora, and the hair--represent not so much an animal inheritance, such as we commonly misrepresent them to be, but a higher and genuinely human development. As none of these structures subserve any clear practical use, it would appear that they must have developed by sexual selection to satisfy the æsthetic demands of the eye.[83] The character and arrangement of the pubic hair, investigated by Eschricht and Voigt more than half a century ago, have been more recently studied by Bergh. As these observers have pointed out, there are various converging hair streams from above and below, the clitoris seeming to be the center towards which they are directed. The hair-covering thus formed is usually ample and, as a rule, is more so in brunettes than in blondes. It is nearly always bent, curly and more or less spirally twisted.[84] There are frequently one or two curls at the commencement of the fissure, rolled outwards, and occasionally a well marked tuft in the middle line. In abundance the pubic hair corresponds with the axillary hair; when one region is defective in hair the other is usually so also. Strong eyebrows also usually indicate a strong development of pubic hair. But the hair of the head usually varies independently, and Bergh found that of 154 women with spare pubic hair 72 had good and often profuse hair on the head. Complete or almost complete absence of pubic hair is in Bergh's experience only found in about 3 per cent. of women; these were all young and blonde.