The given bell shape illustration of course has irritated my eyes, when it has popped up in the right column of the TubeNet.
I don't think, that it is a plain illustration of any real brass instrument. PhotoShop or the like has been involved.
The throath through flare area has been stretched vertically. Still the manipulation is based on a photo of a real instrument. Which one?
Most brass instruments have bell flares with a profile where the tangent of the profile tends to end up perpendicular to the axis of the bell.
Only one national tradition deviates remarkably from this: the French one, where the tangent ends up at an angle of 45° or 60° to the bell axis.
As the French tradition via the Distins and the Bessons was very influential on the British tradition, we also will find such tangent angles on pre-Sovereign British brasses, even on one of the Sovereign Bb cornets.
However the photo manipulation in question rather has taken is base in a photo of a traditional French cor de chasse:
From the horn lists I have heard about these hunting horns having their own playing traditions, but never had heart samples.
Try to listen to La Saint-Hubert at
http://www.journeesdechasse.com/
and you will have your definitions of good musical taste challenged.
Try to click Entrez on that page and then listen to Le Point Du Jour at the bottom of the page coming up.
You won't be less chocked!
But then you have learned about the historical background for the older French French horn playing style and for the older brass band vibrato.
Klaus