IIALFORMATIOXS. 107 



Pygopagi have two umbilical cords which fuse to term a single 

 cord ; coccyx and sacrum are single, rectum and anus usually 

 single ; spinal cord double anteriorly, fused posteriorily form- 

 ing a single filum terminale ; urogenital system usually double. 

 Ventral posterior union may be confined to the pelvic region, 

 (ischiopagus), or it may extend anteriorlv to and including the 

 thoracic cavity, (thoracisischiopagus). The two bodies in ven- 

 tral posterior union are so united that their venter surfaces arc 

 in apposition. Ischiopagi, usually have a single umbilicus and 

 cord ; pelvic organs may be single or multiple ; there is usually 

 no anus. If one of the bodies is small or rudimentary, it is desig- 

 nated a parasite, (ischiopagusparasiticus). Thoracoischiopagi, 

 majr have single or double thoracic viscera ; the abdominal vis- 

 cera are usuallv double. 



Middle union in double monsters occurs on the venter sur- 

 face from the umbilicus and extends anteriorly. There is usu- 

 ally a single umbilicus ; the abdominal viscera is usuallv double ; 

 thoracic viscera single or double, depending upon the area of 

 union ; middle union mav occur at the xiphoid cartilage, (xipho- 

 pagus), involve the entire sternum, fsternopagus) , or the entire 

 thoracic venter surface, (thoracopagus), xiphopagi mav sur^■ive, 

 the "Siamese Twins,'' were of this type. Thoracopagi are fre- 

 quently unequal in size, the smaller one being designated as a 

 parasite. 



Anterior union may be dorsal or ventral or the union may be 

 on the anterior surface of the head. Dorsal, anterior union 

 rarely occurs, the attachment being on the frontal region. These 

 malformations are designated Craniopagi. Ventral anterior 

 union occurs occasional!}'. The union in this type is along the 

 venter cervical region and extends onto the venter thoracic re- 

 gion. The sternum and riesnphagus are single; larynx, trachea 

 and stomach mav be single or doul)Ie; intestine double; there 

 may be two faces or the faces may be fused. Fused-face mon- 

 sters resulting from union of the venter anterior cervical or 

 cephalic regions are called syncephali. 



Incomplete Duplicity is the name applied to those malforma- 

 tions in which the greater part of the body is single, duplica- 

 tion occurring in only a part. The duplicity may involve any 

 part. These malformations are not easily differentiated from 

 malformations resulting from multiplicity of parts as polydacty- 

 lism. 



ASYMMETRic.M. DUPLICITY are thosc malformations resu't- 

 ino- from the development of two separate, dissimilar, unequal 

 an'iao-en of a single ovum, the development of a fertilized polar 



