四肢解構 The incredible human hand and foothd高清在线

both the human hand and foot represent a triumph of complex engineering, exquisitely evolved to perform a range of tasks. 　　Our arms and legs are pentadactyl limbs - they have five digits. 　　When the fist four-legged animals began to move onto the land from the sea around 380 million years ago some had as many as eight digits but the familiar five digit pattern soon became the stan...