REPRODUCTION 567 



paragraph (p. 561) gives rise to four cells each of which develops 

 into a functional spermatozoon. 



The Reproductive Organs of the Female. Each ovary (o, 

 Fig. 153) is a dense oval mass about 3.25 cm. (1.5 inches) in 

 length, 2 cm. (0.75 inch) in width, and 1.27 cm. (0.5 inch) in 

 thickness; it weighs from 4 to 7 grams (60-100 grains). The 

 organs lie in the pelvic cavity enveloped in a fold of peritoneum 

 (the broad ligament), and receive blood-vessels and nerves along 

 one border. From time to time ova reach the surface, burst 

 through the enveloping peritoneum, and are received by the wide 

 fringed aperture, fi, of the oviduct or Fallopian tube, od. This 

 tube narrows towards its inner end, where it communicates with 

 the uterus, and is lined by a mucous membrane, covered by 

 ciliated epithelium; plain muscular tissue is also developed in its 

 wall. The uterus (u, c, Fig. 153) is a hollow organ, with relatively 

 thick muscular walls (left unshaded in the figure) ; it contains the 

 fetus during pregnancy and expels it at birth; it lies in the pelvis 

 between the urinary bladder and the rectum (Fig. 154); the Fal- 

 opian tubes open into its anterior corners. It is free above, but 

 its lower end is attached to and projects into the vagina. In the 

 fully developed virgin state the organ is somewhat pear-shaped, 

 but flattened from before back; about 7.5 cm. (3 inches) in length, 

 5 cm. (2 inches) in breadth at its upper widest part, and 2.5 cm. 

 (1 inch) in thickness; it weighs from 25 to 42 grams (J to 1J oz.). 

 The upper wider portion of the womb is known as its body; the 

 cavity of this is produced at each side to meet the openings of the 

 Fallopian tubes, and narrows below to the neck, or cervix uteri, 

 opposite c (Fig. 153), the communication between neck and body 

 cavities being known as the os internum. Below this the neck 

 dilates somewhat: it forms no part of the cavity in which the em- 

 bryo is retained and nourished. The lowest part of the cervix 

 reaches into the vagina and communicates with it by a transverse 

 aperture, the os uteri. During gestation or pregnancy the fetus 

 develops in the body of the womb, which becomes greatly enlarged 

 and rises high into the abdomen: the virgin womb lies mainly 

 below the level of the bones of the pelvis. 



The chief bulk of the non-gravid uterus consists of a coat of 

 plain muscular tissue, arranged in a thin outer longitudinal layer, 

 and an inner, thicker, consisting of oblique and circular fibers. 



