DUPLICITY. 9 



of a pelvis, with total deficiency of an axis, and of two 

 posterior limbs fused together above as far as the middle 

 of the femora by the skin and soft parts. Hunterian. 



46. A Chick with the imperfect wings and legs of a second 

 Chick attached to the abdominal integuments. 



Hunterian. 



Subclass IV. Heterologous union. 



47. A Duckling with the remains of a second embryo adhering 



in the superior fontanelle, which has not been closed. 

 It consists of a kind of atheromatous tumour, partially oc- 

 cupied by a hernia of the Duckling's brain, with a small 

 but well-developed leg and foot growing from it. 



Hunterian. 



48. A Pigeon with a small accessory wing growing from the 



lower part of the sternum. There is no other trace of a 

 second embryo, and the skin has been reflected to show 

 the union of the limb by muscles and ligament with the 

 sternum. Hunterian. 



Comparing this specimen with No. 47, and in the complete ab- 

 sence of any other means of accounting for the condition, it has 

 been placed in this series, as it seems probable that the limb may 

 be the remains of a second embryo. (See also No. 23.) 



Subseries VI. IN MAMMALS. 



Subclass I. Dichotomy. 



A. Anterior Dichotomy. 

 * In Animals. 



Anterior dichotomy in Mammals rarely extends further back 

 than the basioccipital bone ; it occasionally, however, reaches the 

 dorsal vertebrae. In this respect Mammals present a marked 

 contrast to Birds and Reptiles, in which it usually involves some 

 of the vertebrae at least, It is very rare in the human subject. 



