124 MAMMARY APPARATUS OF THE MAMMALIA 



older embryos, where the nipple primordia are 

 completely developed but still connected to- 

 gether (Fig. 42), the pectoral primordium (p) is 

 seen to be prolonged medioventrally. Shortly 



Fig. 41. Fig. 42. 



Figs. 41 and 42. — Nipple Development of "Sciurus 



VULGARIS," SHOWING MiLK-LlNE. (BrESSLAU. ) 



p, Primary-primordiuni of pectoral nipple ; a,, piimary-primordium of 

 first abdomiual nipple ; a^, primary -primordium of second 

 abdominal nipple. 



afterwards it divides into two primordia — a 

 smaller medial and a larger lateral one (Fig. 

 43, p). But before this division is completed, the 

 first abdominal primordium begins to follow suit 

 (Fig. 43, a). Further, supernumerary primordia 



