95 Histological Studies on the Omasum of the Sheep (Ovis Aries) Amit Poonia 1 , Pawan Kumar 2* and Parveen Kumar 3 Department of Veterinary Anatomy, College of Veterinary Sciences Lala Lajpat Rai University of Veterinary and Animal Sciences, Hisar-125 004 (Haryana) Received: 06 October 2012; Accepted: 15 December 2012 ABSTRACT The present study was conducted on omasum of 10 young sheep of local mixed breed. The omasum presented omasal laminae which were categorized into I, II, III, IV and V on the basis of the length of the laminae and were lined by stratified squamous keratinized epithelium. The lamina propria mucosae was large having loose irregular connective tissue whereas, the lamina muscularis mucosae had longitudinally oriented muscle bundles. These muscle bundles were separated from each other by a comparatively thick inner layer of tunica muscularis in I, II and III laminae. The submucosa was very small having loose irregular connective tissue. Outer longitudinal layer of tunica muscularis was comparatively thinner. Tunica serosa lined by flat cells was comprised of loose irregular connective tissue. Key words: Laminae, Omasum, Sheep Sheep rearing is the most popular among economically weaker population of India and it is considered as “mortgage lifter” for the poor farmers. All the functions of omasum are strongly influenced by various histomorpholoigcal and histochemical factors such as structure of epithelium, blood circulation in the wall and distribution of enzymes. An attempt has been made earlier to study the anatomy and histology of compound stomach of buffalo (Sengar and Singh, 1970) and goat (Chungath et al., 1985) and (Mahesh, 2008). The present study was planned to explore the histological architecture of the omasum. MATERIALS AND METHODS The histological and histochemical study was conducted on ten young sheep (6-9 months age) of either sex of local mixed breed. The stomach along with a small portion of oesophagus and duodenum were procured from the local slaughter house immediately after dressing. Small pieces of tissues were collected from omasal laminae, omasal groove with large papillae and large omasal papillae from each animal. The tissues fixed in 10% neutral buffered formalin solution for 48 hours were processed for routine paraffin technique of light microscopy. The paraffin sections of 5-6  were stained with routine Harris’ hematoxylin and eosin stain, Gomori’s method for reticular fibres, Weigert’s method for elastic fibres, Mallory’s method for iron, Ayoub-Shklar method for keratin and pre- keratin (Luna, 1968) and Crossman’s trichrome method for collagen fibres (Crossman, 1937). An attempt was made to demonstrate mucopolysaccharides by McManus’ method for glycogen (PAS), PAS-Alcian blue method for mucosubstances (pH 2.5), Alcian blue method for mucosubstances (pH 2.5) and diastase digestion method for glycogen (Luna, 1968). RESULTS AND DISCUSSION Omasum: The omasum presented omasal laminae which were categorized into I, II, III, IV and V on the basis of the length of the laminae (Fig. 1) as reported in buffalo and calves (Tiwari and Jamdar, 1970; Taluja and Saigal, 1989) and goats (Mahesh, 2008). However, Chungath et al. (1985) in goat reported only three orders of laminae. The first and second order laminae possessed the papillae whereas third order laminae possessed only a few papillae and in fourth and fifth order laminae, the papillae were absent. All the laminae were lined by stratified squamous keratinized epithelium. The stratum basale cells were consisting of round to oval to elongated nuclei (Fig. 2). Their chromatin material was finely basophilic and distributed in the form of fine dusting throughout the nucleoplasm. These cells contained one to two nucleoli. The cytoplasm was finely granular and eosinophilic. The rest of the layers of stratified squamous keratinized Indian Journal of Veterinary Anatomy 24 (2): 95-98, December 2012 1 M.V.Sc. Scholar; 2 Assoc. Proof.; 3 Asstt. Prof. *Corresponding author: pkumar@llruvas.edu.in