62 MAMMARY APPARATUS OF THE MAMMALIA 



vable. Right and left run two bloodvessels, 

 cutaneous branches of the vasa epigastrica. 

 These in the caudal rea:ion flank an area en- 

 closed by the fibres of the sphincter marsupii, 

 just beginning to develop. In the centre of 

 the area is the transverse section of the navel 



FiG. 21. — Abdominal Wall of Nfav-Born Opossum. 

 (Semon Collection.) 



Micro-photograph 12 diameters. 



Vfiih its three vessels, and you can count on 

 the right six, on the left five, dark spots cor- 

 responding to so many nipple primordia. In the 

 middle behind the navel, where the primordium 

 of the unpaired median nipple would be ex- 

 pected, you find instead a pair of them. 



