Patella present in the living monotremes, the platypus and the echidna. In more primitive tetrapods, including living amphibians and most reptiles (except some Lepidosaurs), the muscle tendons from the upper leg are attached directly to the tibia, and a patella is not present. In 2017 it was discovered that frogs have kneecaps, contrary to what was thought. This raises the possibility that the kneecap arose 400 million years ago when tetrapods first appeared, but that it disappeared in some animals. The word "patella" originated in the late 17th century from the diminutive form of Latin ' or ' or "paten", meaning
Composition of the human body Not all elements which are found in the human body in trace quantities play a role in life. Some of these elements are thought to be simple bystander contaminants without function (examples: caesium, titanium), while many others are thought to be active toxics, depending on amount (cadmium, mercury, radioactives). The possible utility and toxicity of a few elements at levels normally found in the body (aluminium) is debated. Functions have been proposed for trace amounts of cadmium and lead, although these are almost certainly toxic in amounts very much larger than normally found in the body. There is evidence that