ATAVISM. 167 
When the mamma, 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 mamme, furnished with teats. 
3. As nipple-less mammz. 
Such mamme, 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 
mamme, 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- 
