On the development of the lymphatics in the heart of the embryo pig

This problem was approached by way of embryology primarily, because extensive lymphatic injections, in the adult heart, are iwpossible due to numerous valves in the lymphatic vessels.In embryos under 60 mm. in length the valves have not formed and retrograde injection of the cardiac lymphat'ics is quite possible under the proper conditions.Also by observing the origin of the vessels in younger embryos and several further stages in their development it appears evident that observations made on the adult heart can be more rationally interpreted and the solution of the problem will be much nearer complete than if conclusions were drawn from the adult specimens alone.The literature on the nature of the lymphatics of the heart is very scanty.The most pretentious and generally accepted work being that of H. Bock of Munich.Ranvier ('95) comes to the conclusion that there is considerable free space in the myocardium (that is, space between the muscle cells and blood vessels) and that this space is lymphatic in nature.This assumption is based on the fact that pericardial lymphatics can be injected by plunging the needle at random into the myocardium at any point.Thus the intercellular spaces and the lymphatics were supposed to be in direct connection.So the entire heart is considered to be a 'lymphatic sponge,' as Ranvier expressed it.Salvioli injected Berlin blue into the myocardium and made out what he thought were lymphatic vessels which ran in the connective tissue septa between the muscle bundles-but he could find no evidence of their connection with the intercellular spaces as advocated by Ranvier.