In the large pillar forests of planet x, a group of vertebrates, in order to hunt down the fast climbing creatures that inhabit their habitat, rather than developing speed as well, went on another evolutionary path than its fellow vertebrates: they became ambush predators, making use of 2 (or more) spinneret organs to shoot silk at its prey, much like some gnaphosid spiders, with the main difference that their silk is adapted to temporarily affix prey to the surfaces they're clinging on. At times, this group cocoons prey as well, for storaging food during winter.
Now, what would be the most effective location for such spinnerets? If it weaved like a spider I'd go for the rear, but the fact that it uses them almost as guns tells me they should be somewhere closer to the head, maybe even inside the mouth. The closest fiction example I have is, well, Toby's version of spiderman. What would be the most efficient positioning? Could such organs develop naturally in a vertebrate (and not like the transgenic goat wigh spider milk type of developing) to begin with?
NOTE: the creatures are the size of an average Pitbull, are arboreal and quadrupedal.