414 Duplicate Twins and Double Monsters 



and an " os antebrachii/' and in Barkow's fetus there were two radii, a 

 median ulna, and a double hand with the full number of digits. 



A. V. — A continuation of the same cause leads to a complete separa- 

 tion of the two inner arm-components, and allows each to develop as an 

 entire organ. These inner arms are usually perfect in form but often 

 show some defect of development which may easily be due to lack of 

 space and the consequent cramped position in which they must be held. 

 This stage is represented by a large number of cases, and is far more 

 common than the intermediate stage represented by the preceding case. 



Ex. — The Tocci brothers. Eitta-Christina. 



A. "VI. — ^This slight advance on the previous stage is characterized by 

 a rudimentary median leg ; otherwise it is like the last. 



Ex. — Marie-Eosa Drouin. 



A. VII. — In this the median limb has attained a considerable degree 

 of development, this being, from the description of the single case re- 

 corded, of about the same grade as the arm in Barkow's case. 



Ex. — Fisher's case, 1773. 



Here the series ends, since there seem to be no known cases represent- 

 ing the next logical step, that in which the median double leg has sepa- 

 rated into two, leaving two complete components, united by a small 

 isthmus, laterally placed. Xiphopagous twins, like the Siamese brothers, 

 often stretch the connecting bond so much that they can place them- 

 selves laterally, but the natural position of all such is face to face. The 

 same is true to a lesser extent in pygopagous twins. It seems possible to 

 consider that in this series a farther separation might affect either the 

 ventral or the dorsal aspect of the body in such a way as to produce 

 respectively either p3'gopagi or xiphopagi, in which case either would 

 represent the missing stage, but in the present state of our knowledge 

 this cannot be definitely assumed. Thus, in the diagram a space is left 

 for conjoined twins laterally placed, and the series ends with the hypo- 

 thetical case of separate twins laterally related (A. IX). 



B. — Separation from Belov\' Upwards; Components Placed 

 Laterally. 



B. I. — Here may be put individuals in which there is a greater or less 

 doubling of the median pelvic parts, especially the external genitals. 

 Such cases are rare but include both sexes. 



Ex. — Several minor cases of duplicity of the external genitals, col- 

 lected by Ballantyne and Skirving, 94-95. 



B. II. — This is like stage IV of series A, with a median leg in place 



