Ordinarily, the nasal passage passes through the typical reptilian skull from the external naris into the internal naris, through the choanae. This passage is very short in lepidosaurs, but getting to archosauromorphans, it becomes longer: the choanae move further back in the skull, and the internal naris goes with it. This passage becomes nice and long in some taxa, especially birds, where the internal nares are positioned well back in the throat. This gives them lots of room for internal nasal tissues and expansions of the nasopharyngeal diverticulae of the cranial air sacs. And boy, do oviraptorids have lots of cranial air sacs.
But, oviraptorids have extremely short snouts. This generally means they end up not being able to use much of this space. So, instead, oviraptorids fold the nasal passage around. Now what is shown above is a “minimum” length nasal passage hypothesis. There is a longer one, and I personally favor this, but I won’t show it yet. But there are several points to be had:
The external, fleshy naris is positioned outside the skull proper, it is not defined by the position of the bony naris. Instead, you locate it largely through the circumnarial fossae around the bony naris. This, then, becomes the nostril. Here, it is shown in carmine red.
The red arrow tracks the passage through the floor of the anterior nasal chamber, which is quite high (those are VERY large bony nares) and extends to the maxillary antrum, which is largely defined by the medial maxillary fenestrae and positioned between the antorbital fenestrae … in typical theropods. In oviraptorids, the antrum extends further posteriorly, so the nasal passage follows suit. This ends up sending the passage down between the eyeballs, but don’t worry: there’s room. The skull is very wide, even if those eyeballs are huge.
The arrow exits the skull into the floor of the palatal vault, at the anterior end (here) of the internal bony naris. Now, the fleshy internal naris is positioned variably within the bony one, but I am tending to orient the arrow further to the rear, so that it passes along between the jugals a bit more, then heads south.
This, then, is how you fit a nasal passage roughly the length of the skull into 1/3 that distance, and while some dinosaurs have this beat by miles, oviraptorids make a better go at it than many theropods. And recall that I am projecting a conservative length here.
So, while oviraptorids have short little schnozes, they have HUGE noses.