Teeth are many, sharp, and backwardly curved. Head with one pair of backwardly directed orbital (frontal bristles) bristles. These use a formfactor which is backwardly compatible to their respective predecessors. Apple subsequently developed a new protocol AppleShare IP which is not backwardly compatible. EMV was designed to allow cards and terminals to be backwardly compatible with these standards. XMODEM-CRC was designed to be backwardly compatible with XMODEM. The flash shoes are not backwardly interchangeable between models.