STUDIES ON THE MAMMARY GLAND 



I. THE GROWTH AND DISTRIBUTION OF THE MILK-DUCTS AND THE 



DEVELOPMENT OF THE NIPPLE IN THE ALBINO 



RAT FROM BIRTH TO TEN WEEKS OF AGE 



J. A. MYERS 



Fruiit the Institute of Anatonij/, Unlversilij of Minnesota, Minneapolis 



SIX TEXT FIGURES AND FOUR PLATES 



The mammary gland undergoes many important changes from 

 birth to old age. Numerous details in the normal structure of 

 the gland at various stages of its history are still miperfectly 

 known. Because of the lack of anatomical knowledge, patholo- 

 gists are often unable to determine whether a certain condition 

 of the mammary gland is due to a physiological or a pathological 

 change. Moreover, a knowledge of the normal course of devel- 

 opment is necessary as a basis for various lines of experimental 

 work upon the mammary gland. In view of these facts further in- 

 vestigation of the developmental changes in the mammary gland 

 during its life history seems desirable. Hence a series of studies 

 upon this subject has been undertaken. The present paper, 

 which is the first of the series, deals only with the growth and 

 gross relations of the ducts, and the gross development of the 

 nipi)les from the first day to ten weeks after birth In later 

 papers, the prenatal condition as well as various changes involved 

 during pregnancy, lactation, and inA'olution will be considered. 



MATKPvIAL AND TIX'HXKJUE 



The present study is confined to the mammary gland of the 

 albino rat (Mus norvegicus albinus). This form is easily reared 

 in the laboratory and is thus available at all times. Its life cycle 

 is short, so that any desired stage in the history of the mammarj^ 



THE AMKHICAN JOURNAL Or ANATOMY, VOL. li), NO. 3 

 MAY, li)iri 



