chain [L, catena] , 1. a length of several units linked together in a linear pattern, such as a polypeptide chain of amino acids or a chain of atoms forming a chemical molecule. 2. a group of individual bacteria linked together, such as streptococci formed by a chain of cocci. 3. the serial relationship of certain structures essential to function, such as the chain of ossicles in the middle ear. Each of the small bones moves successively in response to vibration of the tympanic membrane, thus transmitting the auditory stimulus to the oval window. 4. a connected series, such as a chain of events.
