The visceral pleura of 12 dogs, eight lambs, nine monkeys and four rabbits was studied by methylene blue immersion. Nerve terminations were found in the pleura of all specimens. The following types of nerve endings and patterns of innervation were observed. (1) Free fiber endings arose from small myelinated fibers and terminated in the caudo-ventral lips of the lobes. The parent fibers of these and all other endings arose, in the lamb, rabbit and dog, from nerve bundles radiating from the hilus onto the inter-lobar and diaphragmatic pleural surfaces. In the monkey, parent fibers arose from a complex hilar plexus of nerve bundles before spreading out within the pleural surfaces. (2) Complex unencapsulated endings were seen in all specimens distributed evenly over the inter-lobar and diaphragmatic pleural surfaces. These arose from myelinated fibers which terminated in two or more complex endings. In the monkey, parent fibers may form an anastomotic network before terminating. (3) In the dog, an “end-net” formation was found which appears to be a type of complex unencapsulated ending. This “end-net” is formed by the anastomosis of the terminal branches of several small myelinated fibers.