Fig. 1

External characteristics of the parapagus dicephalus. a Ventral view showing two heads, with anencephaly in the left twin, a shared thorax with a single umbilical cord, and two normal upper and lower extremities. b Lateral overview showing oblique positioning of the heads. The gluteal cleft of the left twin (black arrowhead) and the three lower extremities (black arrow) are distinguishable. c Detailed right-sided view of the genitalia showing two penises (black arrow), of which the lower-positioned one is hypoplastic. The right perineal raphe (black arrowhead) can be followed toward the anal opening (white arrowhead). d Dorsal overview showing vertical ridge in the midline, the third upper extremity positioned between the heads (black arrow), the gluteal cleft of the right twin (black arrowhead), and the third lower extremity with a dysmorphic foot (white arrowhead). e Detailed view of the male genitalia from the left side showing two penises and the left perineal raphe (black arrowhead), which can be followed toward a small dimple (white arrowhead). f Detailed view of the face of the left twin showing flattening of the face and thickening of the philtrum. g Detailed view of the face of the left twin showing wide inner and outer canthal distance. h Detailed view of the umbilical cord showing three vessels. i Detailed view of the dysmorphic foot of the third middle lower extremity with eight discrete digits, of which a single bigger toe with a split toenail (black arrowhead) is seen