A topographical study of the distribution of end‐plates in the cutaneus pectoris, sartorius, and gastrocnemius muscles of the frog

End‐plate distributions have been determined for three frog muscles of different morphology in order to relate end‐plate topography to spatial muscle structure and nerve branching. Koelle's cholinesterase technique was applied, both on whole muscles and frozen sections. The end‐plates of the short parallel‐fibered cutaneus pectoris muscle appeared to be located in short bands along the nerve branches. The nerve tree is restricted to a zonal area across the middle part of the muscle. Depending on the way the nerve branches, the end‐plate bands form innervation patterns, varying from one single continuous band to multiple distributed bands. In the latter case one frequently observes that different end‐plate bands do not run across the same longitudinal muscle fiber area, although the respective nerve branches run parallel across this area. The long parallel‐fibered sartorius muscle has a wider nerve tree and exhibits the same phenomenon for close parallel nerve branches, but end‐plate bands along parallel nerve branches far apart cover the same muscle fiber area. The end‐plate distribution in the bipennate, short‐fibered gastrocnemius is zonal throughout the muscle except in certain compartments containing tonic fibers. The end‐plate zone centers around the inner aponeurosis about half‐way between the muscle tendon junctions of the fibers and is visible only at the muscle surface where muscle fibers run over their entire length at that surface. The results are of general use in the electrophysiology of neuromuscular transmission because they illustrate how in certain twitch muscles neuromuscular morphology may help to localize end‐plates.