Apex domains cannot have CNAME records.
Question and response
Question
dig 64.214.137.163.in-addr.arpa. NS
Answer
64.214.137.163.in-addr.arpa. 5 NS ns004-geadlrv1gvrvu057.g.d-53.info.
64.214.137.163.in-addr.arpa. 5 NS ns004-geadlrv1gvrvu057.g.d-53.jp.
64.214.137.163.in-addr.arpa. 5 NS ns2.nttcom.ne.jp.
64.214.137.163.in-addr.arpa. 5 NS ns004-geadlrv1gvrvu057.g.d-53.net.
Authority
The response has no authority records.
Additional
ns2.nttcom.ne.jp. 5 A 163.137.224.4
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0