There was no communication of the cranial cavities, but simply fusion of the cranial bones covered by superficial fascia and skin.

Daubenton has seen a case of union at the occiput, but further details are not quoted.
CLASS IV .-- The next class to be considered is that in which the individuals are separate and well formed, except that the point of fusion is a common part, eliminating their individual components in this location.

The pygopagous twins belong in this section.

According to Bateman, twins were born in 1493 at Rome joined back to back, and survived their birth.

The same authority speaks of a female child who was born with "2 bellies, 4 arms, 4 legs, 2 heads, and 2 sets of privates, and was exhibited throughout Italy for gain's sake." The "Biddenden Maids" were born in Biddenden, Kent, in 1100.