It is made out of DFCT as a sheet that wraps around the joint so it won't rip and tear. The inner layer of this is the synovial membrane. It is a sheet of synovial cells (fluid) for lubrication. We need this joint so when the cartilage rubs over the neighbour, there is lubrication to help more around easily. The fluid has the same nutrients as blood and pushes in the cartilage to keep chorodates alive.