Superior Colliculus - Evolution and Comparative Anatomy

Evolution and Comparative Anatomy

The optic tectum is one of the fundamental components of the vertebrate brain, existing across the full range of species from hagfish to human. (See the brain article for background.) Some aspects of the structure are very consistent, including a structure composed of a number of layers, with a dense input from the optic tracts to the superficial layers and another strong input conveying somatosensory input to deeper layers. Other aspects are highly variable, such as the total number of layers (from 3 in the African lungfish to 15 in the goldfish), and the number of different types of cells (from 2 in the lungfish to 27 in the house sparrow). In hagfish, lamprey, and shark it is a relatively small structure, but in teleost fish it is greatly expanded, in some cases becoming the largest structure in the brain. (See the adjoining drawing of a codfish brain.) In amphibians, reptiles, and especially birds it is also a very significant component, but in mammals it is dwarfed by the massive expansion of the cerebral cortex.