There are 16-20 cartilagines tracheales. Cartilagines occupy 2/3 to 3/4 of the circumference of the trachea. (not 1/2) Anyway this is great thread. Good luck!
It's a little weird.. I have this shader up that uses channels 1 and 2. If I UV Map on channel 2, it shows up working fine in my shader. If I try to unwrap, and go to channel 2, it resets the UVs back to use channel 1... it's very odd.