VARIOUS KINDS OF HUMAN TWINS 19 



1. Diplopagi. — These are subdivided into two groups 

 characterized as follows: (a) "each of the two com- 

 ponents complete or nearly so"; (&) "the two com- 

 ponents equal to one another, but each one less than 

 an entire individual." In the first group are included 

 a considerable number of subtypes based on the point 

 of juncture, some being joined at the head, others at 

 the thorax, others at the sacrum. Names have been 

 given to these types as follows: craniopagi, thoracopagi, 

 and pygopagi. They may be back to back, side by 

 side, or face to face. In fact, the point of juncture may 

 be such that they are united so as to face at almost any 

 angle. Yet it must be noted that they are not joined in 

 any haphazard way, but are so placed that they form 

 two bilaterally symmetrical objects. In fact, one is 

 the mirror-image of the other, the plane of the imaginary 

 mirror being that in which the junction exists. A 

 number of types of cosmobia or symmetrical conjoined 

 twins are shown in Figs, i and 2, and are described in 

 the legends. 



2. Autosite and parasite. — Sometimes the parasite 

 is merely a head or a head and arms attached to the 

 autosite at or near the epigastrium or upper part of the 

 abdomen. At other times the parasite consists of legs 

 and part of the lower body, without a head, attached 

 as in the first case. Or, finally, the parasite may be a 

 supernumerary head or face attached to the side or back 

 of the head of the autosite. 



Extreme conditions are those in which the parasite 

 is within the autosite. These form tumors usually in 

 the body cavity. They range from almost complete 

 fetuses to mere masses of tissue sometimes containing 



