FIGURE 1.

The embryonic disk model applied to ventral and lateral conjoined twinning. (a) Schematic representation of the embryonic disks as it develops during gastrulation, prior to the folding process that gives rise to the primordial embryonic body. (b–e) In ventral conjunction, the initial distance between the antero‐posteriorly opposing disk primordia determines to what extend the bodies of the twins shared and subsequently become involved in the process of neo‐axial orientation, which leads to compound structures and organs. (f–h) In lateral conjunction, the disk primordia are positioned next to each other and their initial distance and the angle between their longitudinal axes determines the extend of interaction aplasia, which causes adjacent parts of both bodies not to be formed. See also Table 1 for details and terminology concerning the various conjunction types. Please note that the conditions mentioned here concern arbitrarily defined entities that represent recognizable patterns within a spectral continuum of conjunction types.