33 2 NORMAL HISTOLOGY AND ORGANOGRAPHY. 



centa comes away, it is always at the expense of the 

 uterine mucosa, which leaves a raw, bleeding surface. 

 The uterine muscles at once contract, reducing the 

 uterine cavity and checking the hemorrhage. A 

 normal mucous membrane at once regenerates, the 

 ciliated epithelium and mucous glands developing 

 from remnants of glands that were not entirely ob- 

 literated by the placental growth. As a rule regular 

 menstruation is inaugurated when lactation ceases, 

 but there are exceptions to this. A second preg- 

 nancy may follow without any intervening menstrual 

 period, but this is rare. 



THE MAMMARY GLAND. 



The mammary gland is a skin gland that is present 

 in both sexes. In the second month of embryonic 

 life there is a linear thickening of the skin, extending 

 from each axilla to the groin, and at regular inter- 

 vals in this ridge a series of mammary glands develop 

 in many vertebrates. In the human race only one 

 pair is produced, which represents the fourth or fifth 

 pair of this series. In rare cases accessory mam- 

 mary glands are found in man both above and below 

 the normal pair. 



In childhood the mammary gland is identical in 

 both sexes, but with approaching puberty it enlarges 

 in the female, reaching its highest development at 

 the end of pregnancy. The menopause brings 

 about a retrogression and shrinkage of the organ. 

 The gland is therefore to be considered an accessory 

 sexual organ. 



The mammary gland is a segregation of fifteen to 



