Where do CAR and CDR come from? (the Lisp commands)

''Lisp was originally implemented on the IBM 704 computer, in the late 1950s. The 704 hardware had special support for splitting a 36-bit machine word into four parts, an "address part" and "decrement part" of 15 bits each and a "prefix part" and "tag part" of three bits each.
...
Precursors to Lisp included functions:
car (short for "Contents of the Address part of Register number"),
cdr ("Contents of the Decrement part of Register number")
...
The alternate names first and rest, which date back at least to 1959,[3] are sometimes preferred to car and cdr.'' [source]