The IEEE 802.3 committee specified that every byte in an Ethernet frame must be transmitted with the least significant bit first.
This convention sometimes is called little endian order.
Standards do not specify the order in which bits and bytes are stored within a computer. How-ever, a standard does need to spell out the order in which bits and bytes are transmitted. When computers communicate with one another, each needs to know what to expect when bits arrive across a medium.
Note that transmitting the least significant bit first assures that the first MAC address bit that goes onto a wire is the individual/group bit and the second is the universal/local bit.
For example, if X'C2 is the first byte of an ...