Apex domains cannot have CNAME records.
Question and response
Question
dig higia.mx. NS
Answer
higia.mx. 5 NS ns1.net.mexline.com.
higia.mx. 5 NS ns2.net.mexline.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0