A LITERATURE extending over four centuries cannot be checked experimentally by any one observer. The writer has, therefore, contented himself in this paper with recording the observations of others, and has not attempted too critical a review of their works. Conflicting statements, where they occur, must be judged on their merits, but it should not be forgotten in this connexion that the wide variations found in the venous system as a whole have a parallel in the particular part of that system now under consideration. To individual differences, and to differences between individual veins, must be added those due to age, sex and species, and possibly also others.(I) TERMINOLOGY.(See fig. 1.) The valves of veins have been called by various names, membranGe [155], membranulam, ostiola [1], apophyses membrac&arum [47, p. 1221, membranarum epiphyses [47, p. 357; 147], valvulam and Oty/goeE86t& membran.e [1]. In this last,the word sigmoid refers to the old Greek letter sigma, which was semilunar in shape, like a capital C. In addition to the above names, exilia opercula [115] and f7rav6ta-1ol [132] are terms which some writers have referred to valves.Valves have been divided into two classes, first, those over the entries of trib.utary veins, variously called platismata or platismnatia [123], soupapes [140],
