Comparative anatomical and histological study of spleen in cat (Felis catus) and caucasian squirrel (Sciurus anomalus)

This work aimed to identify the morphological and histological structures of the spleen in the Cat (F. catus) and the Caucasian squirrel (S. anomalus). Eight adult animals of both sexes were used in this study. The weight of the animals was estimated to be between 2.57-4.37 kg in Cat F. catus and 190.3-225.7 g in Caucasian squirrel S. anomalus. The spleen in F. catus and S. anomalus appears dark reddish brown; the shape of F. catus is elongated, tongue-like, with one end widened and tri-rayed. While in the Caucasian squirrel S. anomalus, it appears as tongue-shaped and rounded at both ends, concave on one side, and smaller in size than the spleen of the Cat F. catus. The spleen was found in the abdominal cavity on the left side of the stomach in both studied animals. This work revealed that the spleen in Cat F. catus and the Caucasian squirrel S. anomalus is encased in a thick capsule of connective tissue containing collagen fibers, smooth muscle fibers, blood vessels, nerves, and Fibroblasts. In addition, an outer layer of mesothelial cells covers the capsule. This work also showed that the splenic tissue in the cat (Felis catus) and the Caucasian squirrel (Sciurus anomalus) has white and red pulps. The former is composed of splenic nodules, the peripheral lymphatic sheath (PALS), and the marginal zone. Furthermore, the splenic nodules are distributed randomly throughout the splenic tissue, with many shapes (spherical, irregular, and oval), and appear singly or in clusters of 2-3 nodules. The results also detected the presence of central arterioles in splenic nodules.