Cisterna

A cisterna (plural: cisternae) is any membrane-bound sac. They can be found in the Golgi apparatus and in the endoplasmic reticulum. It is the flattened sac on the branch of the endoplasmic reticulum and the curved sac on the branch of the Golgi apparatus.
Position in cells.
Cisternae are on the trans face of the Golgi apparatus. They are in the cytoplasm next to the endoplasmic reticulum and near the cell nucleus.
Roles.
The cisternae play an important role in the packaging, modification, and transport in the cell. They help the transport of proteins and other enzymes from the Golgi. Cisternae transport proteins in the endoplasmic reticulum to the vesicles of the Golgi apparatus.