Dicephalus

DICEPHALUS (from Greek dis- two and kephale- head), diplocephalus, double monster, a specific type of duplicitas anterior, consisting in the division of the upper part of the embryo and the formation of two heads. Incomplete division of the head, i.e., only of the face, is designated by the term diprosopus (from Greek proso- face). D. is characterized by duplication not only of the head but also of the cervical (and sometimes thoracic) spine. Three types of D. are distinguished: 1) D. dibrachius (2 heads and 2 arms), 2) D. tribrachius (2 heads and 3 arms) and 3) D. tetrabrachius (2 heads and 4 arms; this is the rarest type). The anatomy of internal organs in D. varies in different types of this anomaly, but there are certain common features. Thus, respiratory and digestive organs are always duplicated, there are 4 pleural cavities, although sometimes the middle ones may merge into one. The heart and abdominal cavity in D. dibrachius are single, in D. tetrabrachius they may be duplicated. Monsters of the D. type are usually non-viable: only isolated cases have been described in which D. lived for several days. There is only one reference to a prolonged (over 20 years) life of a monster of the D. tetrabrachius type.