The wall of the fore stomach consists of a non-glandular mucous membrane, a two-layered muscular tunic, and a serosa.
Rumen
- The mucosa forms large tongue shaped or conical papillae. The mucosa has neither gland nor lymph nodules.
- The stratified squamous epithelium is of the cornifying type and the stratum corneum forms relatively thick layer on the summits of the papillae.
- The stratum granulosum and stratum lucidum are more or less continuous.
- Cells of the of stratum lucidum often swells up to become nucleated vesicles, with a cornified wall and non-stailnable cytoplasm.
- The lamina propria consists of a dense filtered of fine collagenous and many elastic fibres. Muscularis mucosa is absent.
- Submucosa is loose and blends with the lamina propria without any line of demarcation.
- Tunica muscularis has two layers – an outer longitudinal and inner circular (of plain muscle).
- The serosa bridges the ruminal grooves, where the subserous connective tissue is thick with fat, nerves and blood vessels.
Reticulum
- Macroscopically the mucous membrane forms permanent folds enclosing 4 or 6 sided spaces or cells.
- Smaller folds subdivide the cells. These folds bear microscopic papillae on their sides.
- The folds and the papillae have a central core of connective tissue and are lined by stratified squamous cornified type of epithelium.
- A dense layer of stratum corneum covers the tip of the papillae and the folds.
- In very large fold a band of smooth muscle fibres occurs running in the same direction as the fold itself.
- Muscularis mucosae are otherwise absent. The two layers of muscular tunic (of plain muscle) follow an oblique course and cross at right angles. A tunica serosa is present.
Omasum
- The mucosa forms numerous folds or Omasal laminae of different sizes. These folds or laminae are studded with numerous papillae.
- Each lamina includes the entire mucosa, muscularis mucosae and submucosa.
- The mucous membrane is lined by stratified squamous epithelium and dense capillary nets are found under the epithelium.
- The muscularis mucosae are distinct and extend into the folds and may occasionally send fibres into the papillae on the laminae.
- The larger folds are composed of tissue, which resembles mucous connective tissue.
- The muscular coat consists of two layers of plain muscle – an outer thin longitudinal layer and inner thick circular layer.
- From the inner layer, bundles extend into the folds so that the large folds show on section, epithelium on both sides deeper to which lies the muscularis mucosae on each side.
- A thin stratum of submucosa separate the muscularis mucosae on each side form the central band of muscular layer derived form the inner circular layer of muscularis.
- At the free edge of the folds the central layer of muscle fibres fuses with the marginal thickening of muscularis mucosae. A serosa is present.
