THE REPRODUCTIVE SYSTEM 



141 



(see Fig. 52). A single median uterus for the accom- 

 modation of a single offspring is the outcome of the 

 reduced family, typical of all perfected arboreal animals, 

 and so typical of the Primates and Man. 



The reduction of the family, and its final result in the 

 production of only a single offspring at a birth, has had 

 its effect also upon the development of the mammary 

 glands. Mammary glands, as is well known, are serial 



FIG. 52. THE TYPE OP UTERUS ASSOCIATED WITH SINGLE 

 PREGNANCY. LARGE UTERINE CHAMBER, No UTERINE 



CORNUA, AND LARGE FALLOPPIAN TUBES. 



The diagram is taken from the human uterus. 



structures occurring upon a definite line the mammary, 

 or milk, line which stretches from the axilla, along the 

 sides of the chest and abdomen, over the inguinal region 

 to the base of the tail (see Fig. 53). At intervals along 

 this line mammary glands are developed in all the 

 Eutherian mammals. The number of functional milk- 

 secreting glands that are developed varies. In Centetes, 

 whose large family we have already noted, twenty-two 

 fully functioning glands eleven on each side of the body 

 are developed. In the domestic sow the large mam- 

 mary series is obvious and well known. 



It is a general rule throughout the mammalian series 



