of Human Monstrosity. 231 



them partially into one substance, without destroying their vitality : 

 and at the same time so exactly applied that a single esophagus 

 is neatly compacted from the divided esophagi of two; a single 

 duodenum from two tortuous tubes, of which the corresponding 

 parts were never in the same plane: that the sterna of the germs 

 should have been exactly cloven in the mid line, and the divided 

 parts then as dextrously united, interchangably, the half of one to 

 the half of the other: that the aorta from one heart should, at any 

 period of its growth, have been violently torn away, and then 

 inserted into the other, the same operations being repeated on 

 that other: that parts so essential to life should thus be decom- 

 posed, and re-united under another shape, seems quite impossible. 

 It was in this revolting form that the difficulties of the question 

 presented themselves to some of the advocates of that opinion 

 which derives the origin of double monsters from an originally 

 monstrous germ. But in the present day, when the successive 

 steps of development are better, though not perfectly understood, 

 they cannot have the same weight. On the contrary the objections 

 are refuted by direct observation, and the suppositions on which 

 they are built are found to be entirely erroneous. 



Before endeavouring to explain the anomalies of the present 

 case, it is necessary that I should refer to what is known of the 

 progress of the embryo from its very earliest moments. And I 

 undertake this task the more readily because there is no work of 

 an English author which gives a detailed and at the same time 

 an accurate account of the process: though very valuable detached 

 observations may be collected from the admirable works of Harvey 

 Needham, Monro, Hunter, Cruickshanks and Home. It is to 

 foreigners that we are indebted for accurate explanations of the 

 membranes of the ovum, of the modes in which the several onra 



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