The lateral neocortical morphotype occupied the lateral most few millimetres of the neocortex from the rhinal sulcus. While 6 cortical layers were evident, the borders between these cortical layers were not as clearly defined as those observed in the medial neocortical morphotype (Fig. 6.2). Layer 1 was again cell sparse, had a few tangentially oriented myelinated fibres, and lacked any structures immunopositive for parvalbumin, calbindin and calretinin; however, an overall dense neuropil staining for calbindin and calretinin was observed. Layer 2 was formed by a distinct band of 2–3 granular cells with the occasional parvalbumin and calretinin immunopositive neuron being observed in P. tetradactylus, but these were absent in E. myurus. Layer 3 was the thickest layer, and again, potential sublamination, evinced by denser myelin and SMI-32 staining, was observed. Neurons immunopositive for parvalbumin, calbindin and calretinin were scattered throughout layer 3 in P. tetradactylus, but were not present in E. myurus. The upper and lower borders of layer 4 were indistinct, but a denser neuropil staining for parvalbumin appeared to correspond with layer 4. In both species a number of parvalbumin immunopositive neurons were observed and in P. tetradactylus a high density of moderately strongly stained calretinin immunopositive neurons was present, but this was lacking in E. myurus. Layer 5 was relatively cell sparse compared to adjacent layers, was myelin dense with tangential fibres and contained the occasional parvalbumin and calbindin immunopositive neuron. In P. tetradactylus a high density of moderately strongly stained calretinin immunopositive neurons was present in layer 5, but this was absent in E. myurus. Layer 6 was again formed by a series of vertically oriented palisades, but compared to the medial neocortical morphotype, these palisades were wider, being 4–6 cells in width, and more loosely associated than in the medial neocortical morphotype. Layer 6 was heavily myelinated, had the occasional parvalbumin, calbindin and calretinin immunopositive neuron, and in P. tetradactylus had a higher density of neuronal structures immunopositive for SMI-32, although this was much weaker in E. myurus. As with the medial neocortical morphotype, the minicolumnar organization was apparent in the Nissl stained sections (Fig. 6.2a, h), however, the compactness and observable tight organization of these minicolumns was not as apparent, especially in E. myurus. In addition, the calretinin staining observed in the lateral neocortical morphotype in P. tetradactylus evinces clear vertical processing, but this staining was absent in E. myurus. Interestingly, it appears that the overall organization of the lateral neocortical morphotype, while similar between species, appears to be more distinctly organized in P. tetradactylus than E. myurus, especially in terms of the calcium binding proteins.

The cingulate cortical morphotype observed in the sengis was very distinctive and had an unusual lamination pattern (Fig. 6.3), something we have not observed in other afrotherian species such as elephants, hyraxes, golden moles, and otter shrews. This cortical morphotype was found on the medial wall of the hemisphere, extending onto the dorsal surface for approximately 2 mm. Layer 1 was typically cell sparse, but was quite dense in tangentially oriented myelinated fibres. A high density neuropil staining was observed for parvalbumin, calbindin and calretinin, with the occasional calretinin immunopositive neuron being observed. Layer 2 was made up of a dense packing of granular cells with a low myelin density, but interesting in P. tetradactylus there was dense calbindin and calretinin neuropil immunoreactivity, but in E. myurus there was only dense calbindin immunoreactivity. Unlike the medial and lateral neocortical morphotypes described above, layer 3 was relatively thin and composed only of a high density of granular cells that formed a distinct band of 200–250 μm in depth. In both species this band was dense with tangentially oriented myelinated fibres and had a sparse neuropil staining for parvalbumin and calbindin. In E. myurus, layer 3 exhibited a more intense neuropil immunoreactivity for calretinin than that seen in P. tetradactylus. In both species of sengi the occasional parvalbumin, calbindin and calretinin immunopositive neuron was observed. Layer 4 was by far the thickest of the layers in the cingulate cortex, and in the transition from the medial neocortical morphotype to the cingulate cortical morphotype, the increase in thickness of layer 4 was evident from the dorsoventral spread of intense parvalbumin neuropil immunoreactivity. As a whole, this thicker layer 4 was myelin dense with both tangential and radial fibres, a higher number of parvalbumin and calbindin immunopositive neurons and a dearth of calretinin immunopositive neurons. Layer 4 also showed intense staining of neural structures for SMI-32. Layer 5 was present as a thin cell sparse region deep to layer 4, but was not a distinct lamina in this region of the cortex. Layer 6 was again made up of palisades, however, these were more loosely organized than in the other cortical morphotypes described above and were made up of 5–7 cells in width. Weak immunostaining for parvalbumin, calbindin, calretinin and SMI-32 distinguished this layer from the more superficial layers. Despite this unusual lamination pattern, the presence of minicolumns and vertical cortical processing were clearly evident with the Nissl stained sections, the radial fascicles in the myelin stained sections and the distinct vertical oriented dendrites of the calbindin immunopositive neurons in layer 4 (Fig. 6.3).

The piriform cortical morphotype was found lateral to the rhinal sulcus and evinced three distinct layers (Fig. 6.4). Layer 1, as in other cortical regions, was cell sparse but possessed a number of tangentially oriented myelinated fibres. For the most part, immunostaining in layer 1 was weak, however, in P. tetradactylus a dense network of SMI-32 immunopositive dendrites was observed. Layer 2 was made up of a dense lamina of tightly packed granular cells, approximately 15 cells in depth. In both species this layer was myelin sparse, an intense parvalbumin neuropil was evident and the very occasional calbindin immunopositive neuron was observed. Interestingly, extraverted calretinin immunpositive neurons were present with dendrites that extended into and ramified within layer 1 (Fig. 6.4e, l). The third layer was the thickest layer and appeared to be composed of a range of neuronal morphologies. In P. tetradactylus this layer was quite dense with myelinated fibres, but in E. myurus the myelin density was lower. Large multipolar parvalbumin immunopositive neurons were present (Fig. 6.4c, j), as were a greater number of smaller multipolar calbindin immunopositive neurons (Fig. 6.4d, k). The occasional small calretinin immunopositive neuron was observed, as well as a moderate general staining of neuronal structures for SMI-32. The staining revealed the possibility of a superficial and deep sublamination of layer 3 based on the distribution of neurons and structures immunopositive for parvalbumin, calbindin, calretinin and SMI-32. Despite only being composed of three layers, evidence for the presence of minicolumnar, or vertical, cortical organization was present, especially with the myelin and calretinin stains.