This obstetrical wax model shows a labor situation in which the fetus is in shoulder presentation or transverse posterior presentation (duplicato corpore delivery). The spinal column is everted and the head rests on the lower part of the trunk (podex). The abdomen of the fetus is wedged in the pelvis. The condition described is identical and subsequent, in the labor sequence, to the one described in item XVIII.36. This type of birth very seldom progresses spontaneously, and occurs only with dead fetuses that have macerated or are very small.

The model was commissioned by Felice Fontana, who was working on the installation of the Museo di Fisica e Storia Naturale of Florence, from the sculptor Giuseppe Ferrini and his assistant Clemente Susini.