the bulbous gland? the dog's penis grows a bulb on the end of it when he is doing it, all the sperm in a packet, and then it does some time-release action that takes up to an hour. I saw it once just when the dogs were still fighting, but the male was developing the bulb, which seemed to be traveling up the shaft, and I guess it grows all the way to the end.
I heard that pigs have a corkscrew shaped penis