They are called "mucous Cysts."
"Special Report on Diseases of Cattle"
U.S. Department of Agriculture J.R. Mohler
The mucous Cysts found in the mouth, udder, and vestibule of cows are samples of this form.
"Special Report on Diseases of Cattle"
U.S. Department of Agriculture J.R. Mohler
These Cysts develop rapidly and may reach the size of a man's head or even larger.
"Special Report on Diseases of Cattle"
U.S. Department of Agriculture J.R. Mohler