Mcrit over wings or not?

[themulleye]

In my books they talk of Mcrit as point on the WINGS where airflow reaches M1.0. However on an aircraft like the 747 airflow will reach M1.0 over the hump before the wings.

So is:

Mcrit the speed when airflow over a point on the WINGS reach M1
OR
Mcrit is the speed when airflow over a ANY point on the aircraft reaches M1.

Thanks