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The Distribution and Size of Retinal Ganglion Cells in Cheirogaleus medius and Tarsius syrichta: Implications for the Evolution of Sensory
 

Summary: The Distribution and Size of Retinal Ganglion Cells in Cheirogaleus
medius and Tarsius syrichta: Implications for the Evolution of Sensory
Systems in Primates
Nicole Tetreault, Atiya Hakeem, and John Allman
Sensory specializations, particularly in the visual system, have been crucial
factors in the evolution of brain and behavior in primates (Allman, 2000). The entire
output of the retina is channeled through the retinal ganglion cells whose axons form the
optic nerve connecting the eye and brain. We have mapped the density of retinal ganglion
cells in flattened retinal whole mounts in the dwarf lemur, Cheirogaleus medius, and the
Philippine tarsier, Tarsius syrichta. Figure 1 illustrates these maps, which reveal that the
ganglion cell density is much lower throughout the retina in dwarf lemur than in the
tarsier. In Figure 2, the data for cross sections near the horizontal meridian are depicted
for the dwarf lemur and tarsier from our data compared with similar cross sections from
the galago (DeBruyn et al., 1980) and mouse lemur (Dkhissi-Benyahya et al, 2001).
These data indicate that the retinal ganglion cell densities as a function of eccentricity are
similar in tarsier, galago and mouse lemur, and that the ganglion cell densities in dwarf
lemur are much lower, particularly near the center of the retina. In Figure 3, we have
added comparable cross sectional data for the diurnal rhesus macaque to illustrate the
enormous increase in ganglion cell density associated with higher acuity in diurnal
anthropoids. This point is further documented in Table 1, which shows peak retinal

  

Source: Allman, John M. - Division of Biology, California Institute of Technology

 

Collections: Biology and Medicine