"Motor responses may be elicited from this entire area by electrostimulation in the rat (Lash- ley, '21, '41; Settlage et al., '49; C. N. Wool- sey, '52, '58; Hall and Lindholm, '74), and the cell and fiber pattern of the entire area is fairly homogeneous (Krieg, '46b; Vaz Ferriera, '51). There is thus little justifi- cation for setting apart separate "associa- tion" cytoarchitectonic fields at the frontal pole." " The cortex in area 6 is the widest and of lowest cell packing density of all frontal fields. A superficial condensation of small pyriform cells demarcates layer 11. Layer V is particularly wide. The largest of its pyramidal cells are in Va. In addition to the prominent radial fiber pattern typical of frontal fields, tangential fiber strata are impregnated in layers 111, IV and V in addi- tion to those in layers VI and I. The cell and fiber densities increase substantially, but without change in pattern of distribu- tion, with rostra1 to caudal progression through field 6 . On the ventro-lateral as- pect of the frontal pole Krieg differentiated a separate field 11 on the basis of reduced cortical width and decreased density of tangential and radial fibers. However, the pattern of cell and fiber architecture is similar to that elsewhere in field 6 with which i t is included in the present parcel- lation. The caudal transition from field 6 to 4 is marked by an increased prominence of layers 111 and IV. Layer V becomes nar- rower; at the same time it becomes more densely cellular, and its pyramidal ele- ments become larger. Both radial and tan- gential fiber components within field 4 are increased and are intermediate in density between those of field 6 and the adjacent densely fibrous parietal region. The cell pattern of field 8 differs from that of 6 in that the condensation of superficial pyra- mids of layer I1 is more conspicuous whereas the granular layer IV is very at- tenuated. The pattern of radial fibers is more dense as is the tangential stratum in layer I. A dense tangential stratum in layer VI merges with the cingulate bundle in the depths of field 8. The character of fields 10 and 11 differs in important re- spects from that of the foregoing frontal fields. In common with other fields along the dorsal shoulder of the rhinal fissure there is little distinction among cellular layers. The supragranular cortical zone of field 10 is uniformly globular without dis- tinction between layers I1 and 111. Though present, layer IV is narrow and of low cell density. Layer V is densely and more uni- formly cellular. The fiber density is low, comprising only a minimally developed stratum in layer VI and a few radial fibers. Field 11 is similar in its cell pattern to field 10, distinguished chiefly by a ten- dency of cells of the supragranular zone to be aggregated into clumps. Field 11 is dis- tinctive, however, for its high density pat- tern of radial fibers. "
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