They seemed to have had individual nervous systems, as when one was pinched the other did not feel it, and while one slept the other was awake.

There must have been some vascular connection, as medicine given to one affected both.
Fig.

36 shows a mode of cartilaginous junction by which each component of a double monster may be virtually independent.
Operations on Conjoined Twins .-- Swingler speaks of two girls joined at the xiphoid cartilage and the umbilicus, the band of union being 1 1/2 inches thick, and running below the middle of it was the umbilical cord, common to both.

They first ligated the cord, which fell off in nine days, and then separated the twins with the bistoury.

They each made early recovery and lived.
In the Ephemerides of 1690 Konig gives a description of two Swiss sisters born in 1689 and united belly to belly, who were separated by means of a ligature and the operation afterward completed by an instrument.