Figure 6. Distribution of intratelencephalic neurons in mammals, reptiles, and birds.

Schematics of the telencephalon of a mouse (left), alligator (middle), and chicken (right). The dorsal telencephalon is shaded in grey. In the mammalian neocortex, the vast majority of excitatory neurons in the upper layers 2 and 3 are intratelencephalic (IT) neurons (blue dots). IT neurons are also interspersed with output neurons in the deep layers. Molecular data suggests IT neurons are present in the alligator cerebral cortex and form a mesopallium in the dorsal DVR. Unlike the arrangement in the neocortex, avian IT neurons form coherent clusters segregated from other major excitatory neuron populations.