360 J. A. MYERS 



pass cephalad. It is evident from the drawing of the surface of 

 the abdomen (fig. 1) that the nipples are arranged on each side 

 so as to form somewhat of an arch. It should be noticed in 

 figure 2 that the arch effect is also carried out by the direction 

 and distribution of the ducts. 



The milk-ducts of late human and rabbit fetuses were divided 

 by Rein ('82) into several subdivisions as follows: (1) the in- 

 flated terminal branches of the 1st, 2d, and 3d orders which to- 

 gether form the outline of the secretory part of the gland; (2) 

 that part extending from these ramifications to the mammillary 

 zone which represents the future lactiferous sinus; (3) the intra- 

 mammillary portion which constitutes the proper excretory duct ; 

 (4) the infundibuliform part which passes through the epidermis. 

 Brouha ('05) was unable to adopt the subdivisions proposed by 

 Rein, because neither at birth nor even in the course of the first 

 month of postnatal life was he able to distinguish any part which 

 was differentiated into a lactiferous sinus. Owing to this fact 

 Brouha suggested and followed a somewhat different subdi- 

 vision. He considers each milk-duct composed of three seg- 

 ments; (1) the intra-epidermal infundibuliform segment; (2) the 

 excretory segment which extends from the preceding to the place 

 of the first bifurcation; (3) the secretory segment, which is com- 

 posed of the succeeding branches. This subdivision Brouha 

 bases upon the later histological characters of the different por- 

 tions of the lactiferous arborization. 



A somewhat different classification of the ducts is used in this 

 paper. That part of the duct passing through the epidermis is 

 called the intra-epidermal portion of the primary duct. That 

 part extending from the epidermis to the first division is desig- 

 nated the pi'imary duct. The ducts resulting from the divisions 

 of the primary ducts are spoken of as the secondary ducts. The 

 secondary ducts divide into the tertiary ducts. The collateral 

 ducts are those given off from the sides of the main ducts. All 

 those ducts which end blindly are called terminal ducts. 



When the various pairs of glands are examined it will be ob- 

 served that for certain featiu'es a single general description can 

 be applied to the ducts of all. However, each varies more or 



