There are lymph nodes in the area you described. I lost my best buddy ever on 11/6/08 to lymphoma, so I am intimately familiar with the lymph nodes. If they are swollen you should see the vet asap. Another area to check is behind the knee in the back legs. These nodes are easy to feel on healthy dogs. I would say that the normal size in an adult dog would be like one of those cap type pencil erasers. Or like the size of a lima or kidney bean. Or smaller. Hard to describe. Anything bigger and I would be waiting at the vets office. There are also lymph nodes in the groin area, but if you have any concern, I would just go see the vet and let them do an exam. Canine Lymphoma is not usually noticed by pet owners until all the nodes are swollen or "blown up". And some owners don't notice it until the Lymph nodes in the sternum are so swollen that their pet is having trouble eating. It is probably nothing, but just be sure....good luck.
While on the subject, Lymphoma is treatable with chemotherapy. I won't bore you with our experience, but I will tell you that it was worth every penny I spent.