Ok, figured it out:
# cat /var/named/chroot/etc/named.conf options { directory "/var/named"; };
zone "internal.mycompany.com" IN { type slave; file "slaves/internal.mycompany.com"; masters { 10.121.42.40 port 53;}; check-names ignore; };
zone "121.10.in-addr.arpa" IN { type slave; file "slaves/10.121"; masters { 10.121.42.40 port 53;}; check-names ignore; };
include "/etc/rndc.key";