Stomach of the Ruminants:

2. Interior Anatomy

A. Ruminoreticulum

I. Rumen

The longitudinal grooves on the outside are represented by corresponding pillars on the inside. The nonglandular mucous membrane of the rumen is covered with cornified stratified squamous epithelium. The mucous membrane forms large conical or tongue-shaped papillae. The papillae are well developed in the ventral sac, the blind sacs and the cranial sac. The pillars and the dorsal sac lack papillae. The rumen communicates with the reticulum through the ruminoreticular opening, which is almost completely surrounded by the ruminoreticular fold