Figure 4.

Comparison of Butler's,⁹⁰ on the left, and Reiner's,⁹⁴ on the right, postulated pallial components in the common stem amniote ancestor of the synapsid radiation leading to mammals and the diapsid radiation leading to sauropsids. Each figure illustrates a schematized transverse hemisection on the right side, with medial to the left. Reiner coined the term proto-DVR for the pallial region constituting V2 and A in sauropsids. As can be seen in comparing the two diagrams, Butler and Reiner agree that the initial pallial expansion of collothalamic-recipient regions was very small and constituted neither a full-blown DVR as seen in extant sauropsids nor a full-blown neocortex as seen in extant mammals. Abbreviations: A, primary auditory pallium; C, collopallium; H, hippocampal pallium; L, lemnopallium; P, piriform cortex; V1, primary visual pallium; V2, secondary visual pallium.