Apex domains cannot have CNAME records.
Question and response
Question
dig 35.in-addr.arpa. NS
Answer
35.in-addr.arpa. 4 NS z.arin.net.
35.in-addr.arpa. 4 NS r.arin.net.
35.in-addr.arpa. 4 NS x.arin.net.
35.in-addr.arpa. 4 NS u.arin.net.
35.in-addr.arpa. 4 NS y.arin.net.
35.in-addr.arpa. 4 NS arin.authdns.ripe.net.
Authority
The response has no authority records.
Additional
r.arin.net. 3 A 199.180.180.63
u.arin.net. 3 A 204.61.216.50
y.arin.net. 3 A 192.82.134.30
z.arin.net. 3 A 199.180.180.63
arin.authdns.ripe.net. 3 A 193.0.9.10
r.arin.net. 3 AAAA 2001:500:f0:0:0:0:0:63
u.arin.net. 3 AAAA 2001:500:14:6050:ad:0:0:1
y.arin.net. 3 AAAA 2001:500:127:0:0:0:0:30
z.arin.net. 3 AAAA 2001:500:f0:0:0:0:0:63
arin.authdns.ripe.net. 3 AAAA 2a13:27c0:30:0:0:0:0:10
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0