Topic summary
Phalanx bones
Extracted from the Wikipedia article Phalanx bone.
Other animals
Most land mammals, including humans, have a 2/3/3/3/3 formula in both the hands (or paws) and feet. Primitive reptiles usually had the formula 2/3/4/4/5, and this pattern, with some modification, remained in many later reptiles and in the mammal-like reptiles. The phalangeal formula in the flippers of cetaceans (marine mammals) varies widely due to hyperphalangy (the increase in number of phalanx bones in the digits). In humpback whales, for example, the phalangeal formula is 0/2/7/7/3; in pilot whales the formula is 1/10/7/2/1.