Four possibilities come to mind. One is that he got a puncture wound from something or someone (such a running into something or getting bitten) a week or so ago and an infection occurred, thanks  to the bacteria and irritation introduced at that time. After a while, an absess formed with pus composed of the bacteria and the white blood cells involved in fighting it. When these get organized, the pus builds up  and caused the area to suddenly start to swell.  As it gets bigger and bigger, the animal often will spike a fever and rub or scratch at it until it breaks if it's not opened surgically before then

A second possibility if it's to one side, it that it could be a salivary gland problem. If a bit of food or something gets lodged in the duct that enables the saliva from one of the salivary glands to empty into the mouth, the saliva will build up in the gland which will enlarge enough to be seen.

If the lump is is on one side and in the area between the end of his jawbone and his neck, then it could be enlarged lymph node. These normally enlarge gradually but sometimes we don't notice this until they reach a certain size. Lymph nodes may enlarge because of infections in the area or as a result of cancer. I consider these the least likely probability in your dog's case based on what you say, but only a thorough physical and complete history could rule them out.

so is it dangerous my 9 week old pit has a lump just beneath his jaw and part of his neck it seems to hert him and he is shaking as if he was cold but know he is not from what you say it sounds like a Lymph node is it cancerous or dangerous should we be worried and take him to get looked at

My dog has the same problem now, what is the most likley possibility that it could be. it is quite large, and i am concerned for my yellow lab. it is now about the size of a tangerine. should we get him help soon?

 

I just found a lump on my dog's throat? What could that be?