The Anatomy of aWOKS'E, 105 



virtue of the fpiral Direction of its Fibres, it is thereby en- 

 abled to bear the frequent Sallies of the Blood in its Expul- 

 fion from the Heart ; and leH thefe Fibres fliould feparate 

 upon any violent Impulfe, the innermoft Coat, though a 

 fine tranfparent Membrane, yet it is wove fo clofe, as to 

 be able to prefcrve the middlemoft, and keep the Blood 

 within its proper Channels. 



It is moreover to be obferved, as the Arteries are conical 

 Channels, and grow gradually fmaller, fo their Coats grow 

 proportionably thinner. And the Coats of <TheCoatsofthe 

 the Veins feem, according to the Opinion of /^^/„j ^ CoTtti- 

 the moft modern Anatomifts, to be only a nuationofthofe 

 Continuation of the Coats of the capillary of the Arteries^ 

 Arteries, refledled back again towards the 

 Heart. But although the Coats of the Veins be the fame 

 with thofe of the Arteries^ yet it is to be taken Notice of, 

 that the mufcular Coats of all the Veins are as thin as in 

 the capillary Arteries ; the Prefllire of the Blood againlt 

 the Sides of the Veins being much weaker than that againlt 

 the Sides of the Arteries, and therefore not requiring its 

 Channels to be fo thick and ftrong. 



The Veinsare not endu'd with Pulfation, as the Arteries,' 

 becaufe the Blood falls into them with a continual Stream 

 from the capillary Arteries, which by reafon of their Small- 

 nefs, have only a very weak, or fcarcely any Motion ; and 

 then as it advances towards the Heart, it moves from a 

 narrow Channel to a wider ; and therefore its Motion 

 would have been extremely languid and flow, had not Na- 

 ture contriv'd feveral Helps to promote its q-j^gj/- 1^ j.„ .r. 

 Pafiage. For that Reafon, as it is the Of, Waives. 

 fice of the Veins to return and carry back 

 all the Blood to the Heart, there is to be feen in mofl of 

 them (efpecially in fuch as have their Direclion upwards) 

 feveral Valves at convenient Diftances, fometimes one, and 

 fometimes more, like fo many half Thimbles ftuck to their 

 Side, with their Mouths towards the Heart ; and as the 

 Blood moves that Way, they are prelled clofe to the Sides 

 of the Veins ; but if it fhould fall back, it muft fill the 

 Valves, and ftop up the Channel, that no Blood can repafe 

 them. Arid befides thefe Valves, it is alfo obfervable, that 

 in many Places where there is a Branch of a Vein, there is 

 an Ai tery lies under it, which by its continual Pulfations, 

 helps to forward the venal Blood towards the Heart ; fo 

 that albeit the Blood moves from?, narrow Channel into a 



wider^ 



