The inferior frontal system, concerned with learning chemotactile discriminations, shows four distinct regions. The posterior buccal lobes contain both large and small cells and are the centre of the system. They receive fibres from the arms (without interweaving), from the lips, and from the buccal mass. They send fibres downwards to the arm centres and backwards to the optic and superior frontal/vertical systems. This is therefore probably both a reflex centre for response to some simple chemotactile stimuli and also the main output pathway for the whole system. In the lateral inferior frontal lobes the fibres from the arms interweave and mix with those from other sources. Their efferent fibres pass to the posterior buccal lobes and to the same destinations as the efferent fibres of the posterior buccal lobes. The organization of the lateral inferior frontal thus allows responses to combinations of chemotactile inputs. The median inferior frontal lobe receives the same input as the lateral inferior frontals, and its interweaving bundles allow for further spreading and combination between afferents. Its efferent axons pass only to the subfrontal lobes. The subfrontal lobes, besides the input from the median inferior frontal lobe, receive fibres from below. Their cells are mostly very small, with axons ending within the lobe A few larger cells with axons running to the posterior buccal lobes carry the output. The tactile system is thus essentially similar to the visual one, with a pair of lower centres (posterior buccal and lateral inferior frontal) and a pair of upper ones (median inferior frontal and subfrontal). Embryologically these all differentiate from a single lobe, and the small cells of the upper lobes form a continuous layer with the relatively fewer small cells of the lower lobes. The main difference between the visual and tactile systems is the absence from the latter of a differentiated region corresponding to the optic lobe. From the evidence of Wells the change that constitutes a memory record occurs in the region of the posterior buccal lobe that contains both large and small cells. This region is under the influence of the circuit through lateral and median inferior frontal and subfrontal lobes.