<Li> Chitterlings, a kind of food, consist of thoroughly washed pig's gut . </Li> <Li> Animal gut was used to make the cord lines in longcase clocks and for fusee movements in bracket clocks, but may be replaced by metal wire . </Li> <Li> The oldest known condoms, from 1640 AD, were made from animal intestine . </Li> <P> Many birds and other animals have a specialised stomach in the digestive tract called a gizzard used for grinding up food . </P>

Which of the following is not an organ of the gastrointestinal tract