The sac like structure between the small intestine and the large intestine in ruminants is:

“Rumen” is the first largest compartment of ruminant’s (grass-eating animal) stomach, where most of the food gathers soon after swallowing and is later brought back to the mouth as cud for thorough chewing.

It is a sac-like structure present between small intestine and large intestine in ruminants.

Depending upon the size of the cow, it can contain up to 25 gallons of material. It serves as a feed storage or holding vat due to its size. Apart from being a storage sac, it also serves as a fermentation vessel.

Hence,  the correct answer is option ‘C’ i.e. Rumen