Forty African giant rats (AGRs), (Cricetomysgambianus-Waterhouse) were used for morphometric, morphologic, histologic and histochemical studies. The rats were sacrificed according to the method of Adeyemo and Oke (1990) and the different segments of the large intestine (caecum, colon and rectum) were weighed, measured and photographs taken. Transverse sections of the different segments of the large intestine were stained with Haematoxylin and Eosin for normal histological studies. For Histochemical studies, the transverse sections were stained with Alcian Blue (AB), Periodic Acid Schiff (PAS) and Alcian Blue-Periodic Acid Schiff (AB-PAS) to determine their nature of secretions. The large intestine was observed to have a mean weight and length of 19.98 ± 0.39 g and 75.57 ± 1.00 cm respectively. The large intestine was observed to be made up of the caecum, colon and rectum, and all had similar basic histological structures, none of them had villi. The mucosal surfaces were smooth with goblet cells. Histochemical studies of the large intestine showed a positive response to AB, PAS, and AB-PAS. The thickening of the tunica muscularis of the colon and rectum was correlated with the temporary storage and expulsion of fecal materials. The presence of large number of mucous secreting cells provided a mucous layer around the fecal pellets facilitating its release and protecting the epithelium.
