In order to meet the increasing protein and income demand in Africa due to the rapid population growth, wildlife, such as the African grasscutter, is currently bred and domesticated as microlivestock. This study is one of the series on the brain morphology of this very large rodent, aimed at providing information that is lacking in the literature. Here, the gross anatomy of the cerebrum and brainstem in nine adult African grasscutters is described. The cerebral cortex was smooth, devoid of gyri and sulci, thus, placing the rodent in the lissencephalic group of mammals. However, blood vessels on the cortex created arterial and venous impressions. The cortex was asymmetrically-tapered oval in shape. The rostral and caudal colliculi were exposed through the cerebral transverse fissure. The rostro-caudal extent of the corpus callosum was from the mid-point of the frontal and parietal lobes, to a point just rostral to the occipital lobe. The rostral colliculi were grossly smaller than the caudal colliculi. The occulomotor and trochlear nerves emerged from the ventral midbrain, rostral to the pons. The pons was exceptionally large; it was pre-trigeminal. On either side of the ventral median fissure of the medulla oblongata were conspicuous pyramids. The trapezoid bodies were also conspicuous. These, and other findings, will be useful in future phylogenetic comparison of rodent brain morphology.

The caudal colliculus serves as an integrative station and switchboard, controlling nucleus of lower auditory pathway and motor‐auditory reflex production. The rostral colliculus coordinates reflexive movement of the head, neck, eye and focus the lens for visual tracking of objects. There is no information comparing mesencephalic tectum among neonates, juveniles and adults of African giant rat (AGR). Hence, this study aimed to compare the gross features and morphometric parameters of mesencephalic tectum postnatally in AGR. The following were found and reported: (a) Paired dorsal tips of caudal colliculi were observed through transverse fissure of the intact brain and so, corpora quadrigemina were partly occluded by cerebral cortex in neonates and juveniles. (b) The lateral and medial geniculate bodies were visible, though the lateral was grossly bigger than the medial in adults and juveniles but,  only the lateral was distinguishable in neonates. (c) Live body weight, absolute brain weight, caudal colliculus width, nose–rump and tail lengths increased as AGRs developed with age; mean values of rostral colliculus weight, caudal colliculus height and weight of caudal colliculus in neonates and juveniles were statistically same; while midbrain weight and rostral colliculus height tends to decrease as rats aged. (d) The mean weight of caudal colliculi and width of rostral colliculi were not affected by age. (e) Caudal colliculi were grossly wider than rostral in juveniles and adults, but not neonates. Established regression formulae are necessary to avoid future sacrifice of this rodent.

The nose is a structurally and functionally complex organ in the upper respiratory tract. It not only serves as the principal organ for the sense of smell, but also functions to efficiently filter, warm, and humidify inhaled air before the air enters the more delicate distal tracheobronchial airways and alveolar parenchyma of the lungs. Despite the volume of published studies on the biology of rodents, there is no information on the gross upper respiratory morphology of the African giant rat (AGR) in the available literature. Hence, this study aimed to examine the anatomy of the turbinates, their meatuses, and the morphometry of the nasal cavity. The following were found and reported in this study: (a) There were three nasal conchae in AGR: the nasoturbinate, which was the largest; the ethmoturbinate, which was composed of one well‐developed ectoturbinate and three well‐developed endoturbinates; and the maxilloturbinate, which was fusiform, short, and branched. (b) Three major meatuses were observed: the dorsal nasal meatus, which was the longest and widest; the middle nasal meatus, which was without limbs but had a deep oval caudal recess; and the ventral nasal meatus, which directly continued caudally into the nasopharyngeal meatus. (c) Four ethmoturbinates with four slit‐like meatuses were observed, each with dorsal and ventral limbs; the first contacted the middle nasal meatus but not the nasopharyngeal meatus. (d) There were three paranasal sinuses: one sphenoid, two frontal, and two palatine sinuses. The data obtained are relevant to pathologists and eco‐morphologists, considering the burrowing habitat and behaviors of AGR, and provide baseline data for more investigative studies.

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This study postnally compared the cytoarchitecture of inferior olivary nucleus, dorsal and medial nuclei of corpus trapezoidium and; lateral nucleus of reticular formation in African giant rat (AGR). Thirty captive; apparently healthy AGRs consisting ten each of neonates, juveniles and adults were used. Following sedation, euthanasia was achieved by perfusion of 4% paraformaldehyde via left ventricle; head was cut and fixed for three days in 10% formaldehyde before harvesting the brain. Normal histological procedure was performed and tissues stained with Thionin and Haematoxylin-Eosin stains. The following were found: (a) The fibre shaft of inferior olivary nucleus was characterized by radial glial cells in neonates; neurons formed with undivided nucleus in juveniles; three major subnuclei of inferior olive principal, inferior olive dorsal, and inferior olive medial and two minor subnuclei of inferior olive ventrolateral protrusion and inferior olive Beta in adults. (b) The dorsal nucleus of corpus trapezoidium had oligodendrocytes in their nucleus and thick axons in neurons of all age groups. (c) There were numerous immature migrating neurons of radial glial fiber shaft within extracellular matrix of lateral nucleus of reticular formation in neonates, with numerous blood vessels in all age groups. (d) The medial trapezoid body was characterized by numerous giant pyramidal cells in adults. The relatively poor, improved and dominant acoustic structures in neonates, juveniles and adults respectively; with their visual structures generally poorly developed, though better in adults, is an indication that adults have better audition and vision followed by juveniles and lastly neonates.