Answer:
The reduction of friction between the parietal and visceral surfaces of an internal cavity is the function of serous fluid.
Step-by-step explanation:
Between the parietal layer and visceral layer of an internal cavity there is serous fluid that reduces the friction between these two surfaces and allows an easier movement of the parietal and visceral layers. The serous fluid is produced by serous glands that are in the parietal and visceral membrane.