That is the remains of the windscreen drainage channel. Its purpose in life is to funnel the water coming off the windscreen down little tubes and out onto the road. No drainage channel and you could end up with lots of water falling on your feet as it will find its way into the car via the heater.
So, when I presume that the large, round hole at the left is the heater air intake, and since I'm living in a climate that rarely gets below 25 degrees Celsius (77F), would it help to remain dry feet if I just placed a plastic lid from a paint bucket or other container over said hole?
You may consider stopping by a salvage yard. Very few people damage that parts so it shoudl be inexpensive and will help keep damaging things (dirt, squirells, etc) from getting into your HVAC. Many 850 owerns have to remove their entire dashboard to repalce the AC evaporator as they had no filter over that hole. If you car has a filter you have less reason to worry.