Distribution of small and medium‐sized ganglion cells in the cat's retina

The distributions of small and medium‐sized ganglion cells in the cat's retina have been studied. The soma size ranges of ganglion cells projecting to the superior colliculus and the A‐laminae of the dorsal lateral geniculate nucleus were determined by the retrograde transport of horseradish peroxidase. Confirming previous work, the results suggest a division of the overall soma population into large, medium and small ranges. The large somas are the cell bodies of α‐ or Y‐cells; the small somas are the cell bodies of γ‐ or W‐cells, most of which project to the superior colliculus; and the medium‐sized somas include the cell bodies of β‐ or X‐cells and of γ‐ or W‐cells, most of which project to the forebrain. The small‐soma (collicular‐projecting) cells have a strongly streaky distribution, i.e., the isodensity lines in a map of their distribution are markedly elongated horizontally. These cells form the principal component of the visual streak, especially in nasal retina. The medium‐soma (forebrain‐projecting) cells also show some streakiness, i.e., their isodensity lines are also elongated horizontally, but less markedly than for small cells. The results also show differences between nasal and temporal retina in the distributions of medium‐sized and small somas. It is suggested that the patterns of distribution of small and medium cells may be reflected in the topography of visual centres of the midbrain and forebrain, respectively.