The vocal tract
adapted from Ladefoged, A Course in Phonetics (3rd ed.): 4, 6
 

The positions of the vocal organs in the bilabial stop in "buy"
from Ladefoged, A Course in Phonetics (3rd ed.): 9

The position of the vocal organs during the bilabial nasal stop in "my"
from Ladefoged, A Course in Phonetics (3rd ed.): 9