B737-300/oxygen system

I have not found supernumerary compartment for b737-300 so what is the supernumerary oxygen mask in b737-300? Is it the same as observer oxygen mask?

I believe the supernumerary (stupid name) is only found on wide-body aircraft. It is a small area right behind the cockpit where extra jump seats (or possibly sleeping quarters are located).

On the 737, there is a galley, flight attendant seating area, and a lav behind the cockpit. Those would not be considered as part of a supernumerary. On cargo aircraft..... the shipping containers fill that space.

On the 767, all supernumerary seats have the standard "box mounted" oxygen masks with the inflatable straps. These are the same units used by the pilots.

The only image I have is:
  
     
  
The FedEx aircraft that I worked on had full-face masks that covered both the mouth and eyes. I've only seen these on FedEx aircraft. They were not available in the jump-seat positions.
 
 

I could be wrong on the Supernumerary area on passenger jets. I don't work on people haulers, but I did find this image on the internet. Possibly the front galley, lav, and attendant seats would considered the supernumerary???

Of the planes I've flown on, I've never seen the box oxy masks in this area.
  
     
 

     
 

Is it corresponding to 1'st/2'nd observer or otherwise to the captain/first officer?

All oxygen masks in cockpit would be the box mount type.

I haven't seen otherwise.

My apology for the confusion, what I was asking is whether the last photo that you sent is corresponding to observer mask in b737-300?

I don't have access to 737's.
This should be the same box though.
Even for observer.