part of outer medulla medulla layer M3 stratum M3 L3 layer FBbt:00040028 medulla layer 3 Third most lateral layer of the medulla. It is defined by the proximal border of the lamina monopolar neuron L2 arborization to that of the lamina neuron L3 terminal (Fischbach and Dittrich, 1989). In the literature there are two methods for describing spatial location of neurons in the visual system: distal-proximal (e.g. Fischbach and Dittrich, 1989), and medial-lateral (e.g. Ito et al., 2014), both meaning outer and inner, and refer to the distance of a structure along the visual pathway relative to the center of the brain. Currently we will adopt the classical 'distal-proximal'. FBbt:00003752 fly_anatomy.ontology VFB:FBbt_00003752 medulla layer