The retroperitoneum is the part of the abdominal cavity that lies between the posterior parietal peritoneum and anterior to the transversalis fascia. It is divided into three spaces by the perirenal fascia and is best visualised using CT or MRI.
Transparency is a trait shared by all living glass frogs. In some species though, such as the Condor Glass Frog (Centrolene condor), the ventral peritoneum is white anteriorly, obscuring the heart and liver. Photo by Alejandro Arteaga.