title: Topographical organisation of the retina in a monotreme: Australian spiny anteater Tachyglossus aculeatus.
abstract: The topography of the ganglion cell layer of the retina has been examined in the spiny anteater or echidna, Tachyglossus aculeatus. The retina measures about 70 mm2 in area and contains approximately 60,000 ganglion cells. The somas of the cells do not form distinct size groupings, as they do in other mammals, where the size groupings are related to functional differences. There is only a weak gradient in the density of ganglion cells between central and peripheral regions of the retina. In particular, there is no sign of a localised concentration of cells, such as at the fovea or area centralis of other species, and only very weak evidence of a visual streak. There is thus very little regional variation in the structure of the echidna retina, less than in any mammal previously studied. Implications for the understanding of comparative retinal topography are discussed.
mesh_terms: D000717:Anatomy, Comparative; D000818:Animals; D005123:Eye / Q000033:anatomy & histology; D008322:Mammals / Q000033:anatomy & histology; D009007:Monotremata / Q000033:anatomy & histology*; D010802:Phylogeny; D012160:Retina / Q000648:ultrastructure*; D012165:Retinal Ganglion Cells / Q000648:ultrastructure*; D004442:Tachyglossidae / Q000033:anatomy & histology*