No. 557] INHERITANCE OF MAMM2E IN SWINE 



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but have the single nipples on opposite sides. The third 

 type is where no normal pair divides the two triangles 

 and two mammae on one side balance three on the other. 

 In this case, where more than two triangles are present, 

 three nipples on one side may balance four opposite or 

 four may balance five. This last condition occurred in 

 only two cases. The fourth type is doubtful and difficult 

 to describe. It is as though the two triangles have their 

 bases on opposite sides of the animal, but have one side in 

 juxtaposition with the corresponding side of the other. 

 In other words, two of the mammae form the sides of two 

 oppositely facing triangles and give a two-balancing-two 

 effect. The mammae on one side are opposite a point 

 intermediate between those on the other. This effect may 

 possibly be brought about by a combination of the sup- 

 pressed nipple and triangle type as well. In seven indi- 

 viduals the triangle and suppressed nipple were found on 

 the same animal, separated by one or more normal pairs. 



There sometimes appears a pattern in which the mam- 

 mae of one side are set ahead of the points where they 

 commonly occur, as though one lateral row were pushed 

 slightly forward. This may be characteristic of the entire 

 mammary series or of only one or two pairs. The ar- 

 rangement is seldom so distorted that the identity of the 

 pairs is lost, but occasionally it approaches the fourth 

 compound type of triangle just discussed. A suggestion 

 has been offered that this distortion may be due to the 

 position of the fetus during pregnancy, so that when the 

 abdominal walls grow together, the mammae do not lie 

 exactly opposite. An objection to this is that not only 

 would the abdomen show the asymmetry, but also the ribs 

 and sides. No observations were made on this point, but 

 to the writer the explanation offered seems doubtful. 



The Seat of Greatest Variation—For convenience in 

 description, the pairs of mammae may be numbered from 

 the most forward pair to the rear. Considering the first 

 pair and inguinal pair as constant, the mamma? of the 

 intervening region were tabulated by number. This 



