No abstract

Cricetomys gambianus is a rat that lives principally in burrows, coming out at night in search of food. The design and structure of the lower respiratory system reflects its oxygen and metabolic demand which can be attributed to its habitat. A morphological and morphometric investigation of its lower respiratory system was undertaken to document the normal anatomical features and assess its morpho-functional paradigm. Specifically, an anatomical detail of the lungs and conductive airway was described, the structures being elucidated by dissection and radiography. Evaluation of dissected specimens showed that tracheal cartilages ranged from 21 to 33 rings with an average of 25.5. They exhibited a random pattern of anastomoses between adjacent rings. Transverse diameters of the principal bronchus in the male and female rats were 3.767 and 3.759 mm respectively. The right lung consisted of four lobes while the left lung was not lobed. Bronchogram revealed that lung lobation corresponded with bronchial tree division. Inter-lobar fissures were absent on the right lung except for the ventral boarder separating the cranial lobe from the caudal lobe. The entire lungs provided stability to the heart in situ, through the cardiac notch. This study also included correlation analysis of the dimensions, weights and volumes of the lower respiratory organs with the nose-rump length and body weight of 18 African giant pouched rats of both sexes. The relationship of the anatomy of the lower respiratory system of the rodent to the oxygen tension in their burrow and to their energy utilization is discussed.

A gross morphological study of the brain of the African giant pouched rat (Cricetomys gambianus Waterhouse, 1840) was undertaken in order to document its normal features and assess the structure-function paradigm. The study was conducted by direct observation of 29 adult African giant pouched rats' brains. In the telencephalon, the cerebral cortex was devoid of prominent gyri and sulci, but the large olfactory bulb and tract relaying impulses to the olfactory cortex were very prominent. The large size of the olfactory bulb correlated with the established sharp olfactory acuity of the rodent. In the mesencephalic tectum, the caudal colliculi were bigger than the rostral colliculi, indicating a more acute sense of hearing than sight. In the metencephalon, the cerebellar vermis, the flocculus and the paraflocculus were highly coiled and, thus, well developed. The myelencephalon revealed a better organised ventral surface than dorsal surface; the cuneate fascicle, the intermediate sulcus and the lateral sulcus were not evident on the dorsal surface, but there were clearly visible pyramids and olivary prominence on the ventral surface. In conclusion, the highly coiled cerebellar vermis, flocculus and paraflocculus, as well as the conspicuous pyramids and olivary prominence are indicative of a good motor coordination and balance in the African giant pouched rat.

Forty African Giant Rats (AGRs) were used for the present studies. The mean weight and length of the esophagus were 1.39 g (± 0.08) and 11.78 cm (± 0.53) respectively. These values accounted for 0.13 % and 5.5 % of the weight and length of the gastrointestinal tract, respecttively. Grossly the esophagus was observed to lie dorsal to the trachea throughout its length. The epithelial lining of the esophagus was observed to be made up of nonkeratinized stratified squamous cells. The lamina muscularis and mucous glands were absent. Histochemical studies revealed that the esophagus was Alcian Blue (AB), Periodic Acid Schiff (PAS) and Alcian Blue-Periodic Acid Schiff (AB-PAS) negative.

Anatomy of the mystacial vibrissae in the African giant pouched rat was investigated to establish the role played by these structures in the adaptation of the rodent to its subterranean environment. Gross morphology was based on direct observation of the mystacial vibrissae with the naked eyes, while histology was based on light microscopic examination of the same structure stained with haematoxylin and eosin (H/E), Masson's trichrome (MT) and Masson-Fontana reducing method for melanin. The mystacial vibrissae were aligned in 5-6 rows on each side of the face. The length increased rostrocaudally in each row. The mean number of vibrissae was 55.29 (± 3.42). The vibrissal folliclesinus complex extended into the reticular layer of the dermis. In the proximal part of the sinus, trabeculae of connective tissues connected the internal and external dermal sheaths. The most distal part of the sinus contained blood vessels. The external dermal sheaths were thick and held in position by muscle fibres. Mean thickness of the cortex and medulla in the complex were 1.626 µm (± 0.110) and 0.775 µm (± 0.057), respectively. The thick external dermal sheaths were laden with mechanoreceptors. The thick cortex provided the needed elasticity necessary for touch and sensation. In conclusion, the well developed mystacial vibrissa in the African giant pouched rat is an important compensation for poor vision, necessary for an effective adaptation.