Mitral sac

From Memory Alpha, the free Star Trek reference.

The mitral sac is a specialized structure on Ocampa females that serves as a reproductive equivalent for the Human uterus. It is found on the upper back and first appears as a growth that hallmarks the arrival of the elogium. Delivery is through the sac wall, typically with the mother in a standing position and holding onto an overhead bar for support. (VOY: "Elogium", "Before and After")