It seems obvious that this is a perverted description of the right auricle, and that Reid had no idea of the pulmonary artery as a distinct structure. "The third vessel is arteria venalis. It is called an artery because it carrieth arterial blood, but a vein because it hath a single coat as a vein. It ariseth from the upper part of the left ventricle of the heart, and is implanted into the substance of the lungs by the left side of the windpipe." This in like manner appears to be the left auricle and the pulmonary veins. "The vena arterialis hath three valves called sigmoides from the figure of the great sigma, which answereth the Latin S, the figure is this, C. They look from within outwards, to let out the blood but to hinder the return of the same. "The arteria venalis hath two valves called mitrales, because they are like a bishop's mitre. They look from without inward to let in blood carried from the vena arterialis. They are bigger than those of vena cava and have longer filaments and to strengthen them many fleshy snippets are joined together. "It hath two valves only that the fuliginous vapours might the more readily be discharged." Reid, like all his contemporaries, had a glimmering of the lesser circulation, for he says: "First the blood is carried by vena arterialis and from hence to arteria venalis by sundry anastomoses, and from hence to the left ventricle of the heart. Where being made spirituous it is sent by the aorta to impart life to the whole body. "One thing is to be noted that no air in its proper substance is carried to the heart; for the blood contained in these two vessels is sufficiently cooled by the bronchia passing between them.... One thing is to be noted, that in arteria venosa a little below the valves there is found a little valve ever open. It being removed, there appeareth a hole by the which the blood passeth freely from the vena cava to it and returneth by reason of this anastomosis that the blood in the veins may be animate." This is a description of the foramen ovale and its use. Such a comparison with the work of a contemporary teacher in the same town shows how immeasurable was the advance made by Harvey. It only remains to show what has been done since his death to perfect our knowledge of the heart and of the circulation. The use of the microscope by Malpighi in 1661 gave an insight into the true nature of the porosities by which the blood passed from the terminal arteries to the commencing veins in the lungs and proved them to be vessels. The capillary circulation was still further investigated by Leeuwenhoek in 1674 who described it as it is seen in the web of a frog's foot, and in other transparent membranes; Blankaart in 1676, William Cowper in 1697, and afterwards Ruysch, studied the arrangement of the capillaries by means of injection. In 1664 Stenson demonstrated that the heart was a purely muscular organ.