262 THE VITAL lUNCTIONS. 



ternal pressure, occasionally applied to the veins, 

 assists in promoting the flow of blood towards the 

 3g5 heart ; and hence the effects of exer- 



cise in accelerating the circulation. 

 Valves are more especially provided 

 in the veins which pass over the 

 muscles of the extremities, or which 

 run immediately beneath the skin ; 

 f while they are not found in the more 

 internal veins belonging to the viscera, 

 which are less exposed to unequal 

 pressure. These valves are delineated 

 in Fig. 365, which represents the interior of one of 

 the large veins. 



The situation and structure of the valves be- 

 longing to the hydra vdic apparatus of the circulation 

 furnish as unequivocal proofs of design as any that 

 can be adduced. It vras the observation of these 

 valves that first suggested to the mind of Harvey 

 the train of reflexions which led him to the dis- 

 covery of the real course of the blood in the veins, 

 the arteries, and the heart. This great discovery 

 was one of the earliest fruits of the active and 

 rational spirit of inquiry, which at the era of 

 Bacon's writings, was beginning to awaken the 

 human mind from its long night of slumber, and to 

 dissipate the darkness which had, for so many 

 ages, overshadowed the regions of philosophy and 

 science. We cannot but feel a pride, as English- 

 men, in the recollection, that a discovery of such 

 vast importance as that of the circulation of the 

 blood, which has led to nearly all the modern im- 

 provements in the medical art, was made by our 

 own countryman, whose name will for ever live in 



