Dissected frog. Illustration of a pinned laboratory frog with its abdomen dissected to reveal its heart, lungs and digestive system. In the upper abdomen is the heart (small, red) positioned between the lungs (pink, spongy). Directly beneath the lungs is a layer of muscle (thin, pink), the diaphragm. In the lower abdomen is the liver (triangular, brown) and the stomach (pink). Leading from the stomach are the much folded tubes of the small and large intestines.