GENERAL PATHOLOGY 387 



cording to Darwin's investigations, the deformities are not 

 confined to Europeans but occur in negroes and other races. 

 In animals with four toes on their fore-feet, a fifth super- 

 numerary toe has often been observed ; the deformity is still 

 more common on the posterior extremities. Dorking fowls 

 have five claws on their feet ; dogs and cats, the large newt 

 and the frog are often seen to have six toes on their hind- 

 feet. 1 



Supernumerary breasts are not uncommon in women. 

 They are generally symmetrically placed, but may occur 

 irregularly on any part of the body, e.g., the shoulder, thigh 

 or axilla. They frequently secrete milk. 2 In domestic animals' 

 supernumerary udders the cause is found in the abnormal 

 activity of two usually rudimentary teats ; Darwin quotes 

 instances of a sheep with four, and a cow with six teats. 



Another form of this kind of deformity is seen in " mon- 



c b a 



FIG. 197. Supernumerary digits, a and b, in the hand ; c, in the foot. (Ranke.) 



sters," which are produced by the division, or duplication, of 

 the primary layers of cells. They occur both in men and 

 animals, and when they survive are exhibited in shows, and 

 when incapable of survival find their way into museums of 

 pathological anatomy. The division may begin either at the 

 cephalic or caudal end of the embryo, or at both simultane- 

 ously. This explanation is recent ; formerly it was supposed 

 that double monsters arose from the junction of two originally 

 separate embryos, developed from -separate ova. If the divi- 

 sion begins at the cephalic end, monsters are produced with 

 two heads, two faces or two heads and two thoraces (Plate IV., 

 fig. c) ; or with two heads and bodies and four lower extremities, 

 double men only united by the sacrum and rectum (Plate IV., 

 fig. a). When the division begins at the caudal end, either a 

 monster with double lower limbs is formed, with two pelves 



1 Darwin, loc. cit., iv., p. 14. 2 Ibid., iv., p. 65. 



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