ATAVISM. 167 



When the mammae, or nipples, are increased beyond 

 the number normal to a given mammal, they are said 

 to be accessory or supernumerary, and occur in three 

 forms : 



1 . As nipples or teats. 



2. As mammae, furnished with teats. 



3. As nipple-less mammae. 



Such mammae, or nipples, may be due to atavism, or 

 arise by dichotomy of a normal gland, or occur as a 

 spontaneous variation or " sport." 



Notwithstanding the scanty evidence at the disposal 

 of Darwin when he wrote " The Descent of Man," he 

 regarded supernumerary mammary glands as reversions, 

 although he considered the opinion weakened by their 

 occurrence on the thigh and back. Since then our 

 knowledge on this subject has increased, and has had 

 the effect of strengthening Darwin's opinion. We will 

 first discuss those examples which may be safely 

 regarded as atavistic. From what has been already 

 stated regarding the ventral disposition of these glands, 

 their association with the deep epigastric arteries, and 

 subsequent suppression in the pectoral or abdominal 

 regions, it would be necessarily inferred that accessory 

 mammae, or nipples, would reappear in such situations 

 most frequently ; this is precisely the case. So fre- 

 quently are supernumerary nipples present in the human 

 subject that Dr. Mitchell Bruce in three years saw sixty- 

 five examples. Among 207 men examined consecu- 

 tively, nine per cent, had an extra nipple, and of 104 

 women, four per cent. These observations have induced 

 other observers to look into the question, with a con- 



