The College of Physicians of Philadelphia Digital Library

Twins, Conjoined Thoracopagus

About This Item


Twins, Conjoined Thoracopagus


Congenital Abnormalities
Cleft Lip
Twins, Conjoined


Like many conjoined twins, these two boys were stillborn. Staff at a medical school found the jar hidden away in a closet and donated it to the Mütter Museum. Gretchen Worden (1947–2004), the late director of the Museum, who was fascinated by conjoined twins, nicknamed them Jim and James.

Conjoined twins are rare, occurring in only 1 out of every 200,000 live births. Identical twins form when a single fertilized egg divides into two parts, which then grow into separate embryos. If the egg does not fully divide, the embryo begins to split into twins, but does not completely separate. The twin fetuses develop with their skin and some internal organs fused together.

Death rates are high. About 40 to 60 percent of conjoined twins are stillborn; approximately 35 percent live for only one day after birth. If twins do survive birth, they have difficult lives. Modern medicine makes surgical separations possible in some cases, but the operations, which often attract international media attention, are long and complex. Sometimes, difficult decisions are necessary; if major organs are shared, one twin may need to be sacrificed so that the other can live.

These twins are the thoracopagus type, joined at the upper part of the torso and sharing a heart. About 40 percent of conjoined twins are thoracopagus. Twins connected at the lower abdomen (omphalopagus, 33 percent) may share a liver, digestive system, or genitals. A much rarer connection type is craniopagus (6 percent), in which the bodies are separated but the skulls are fused. Chang and Eng Bunker (1811–1874), the famous “Siamese” (actually Thai-American) conjoined twins, were joined at the abdomen by a band of cartilage. Their shared liver and a death cast of their bodies are on display at the Mütter Museum.


Digitized by the Mütter Museum of The College of Physicians of Philadelphia






19th Century

Original Format

Human tissue, glass container, fluid


“Twins, Conjoined Thoracopagus,” The College of Physicians of Philadelphia Digital Library, accessed May 28, 2023,