162 EVOLUTION AND DISEASE. 
instances dichotomy is responsible for the abnormality, 
and it is only after careful dissection by an experienced 
anatomist that it is possible to determine to which of 
these causes the accessory digit or digits can be ascribed. 
Supernumerary Mamme and Nipples—lit is so diffi- 
cult to distinguish atavistic phenomena from counter- 
feit manifestations that the great need for care in 
this direction will be further illustrated by discussing 
supernumerary mamme and nipples. Up to the present 
time accessory mamme, nipples, or teats, have been 
reported on reliable authority in the following situa- 
tions :—the anterior wall of the chest, abdomen, axilla, 
arm, shoulder, the cheek, buttock, and even in ovarian 
dermoid cysts. If we accept unreservedly, that super- 
numerary mammez are always atavistic, we force ourselves 
into the absurd position of imagining ancestors better 
supplied with milk-glands than even Diana of Ephesus ; 
or if we protect our opinion by stating it in this way :— 
When a mamma occurs in an abnormal situation in man, 
but corresponds to the normal situation of the mamma 
in some lower animal of our class, it is then atavistic, we 
save ourselves much trouble. 
In a few cases the guess would be correct, but in most 
it would be erroneous, and such loose methods of deter- 
mining the nature of abnormal organs will in the long 
run lead to much confusion. At the outset we are faced 
by the question, What is a mamma? A mamma is a 
collection of modified sebaceous glands secreting milk, 
and having close relation to the function of reproduction. 
As a rule such glands are furnished with a cutaneous 
papilla, known as the nipple, or teat, which is either 
