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 Composition of the human body Body composition may be analyzed in terms of molecular type e.g., water, protein, connective tissue, fats (or lipids), hydroxylapatite (in bones), carbohydrates (such as glycogen and glucose) and DNA. In terms of tissue type, the body may be analyzed into water, fat, muscle, bone, etc. In terms of cell type, the body contains hundreds of different types of cells, but notably, the largest "number" of cells contained in a human body (though not the largest mass of cells) are not human cells, but bacteria residing in the normal human gastrointestinal tract. Almost 99% of the