On Muscular Motion and Animal Spirits 241 



not imagine how the extravasated blood could enter 

 the very minute mouths of the veins ; for if the blood 

 were diffused through the mass of the muscle it would 

 seem that the ultimate ramifications of the arteries 

 and veins would be compressed by the blood surround- 

 ing them, so that the blood would not be able to enter 

 the mouths of the veins, as they would be closed by 

 that compression. Further, it is plain that the blood 

 is not extravasated in the muscles, because the blood 

 coming to a muscle does not all rush out if the muscle 

 is wounded, but this would happen if the blood were ex- 

 travasated and diffused through the mass of the muscle. 



So that as to the transit of the blood through the 

 muscles it is right that we should hold that the 

 capillary veins and arteries are united by vessels of 

 some different kind, so that there is a sort of con- 

 tinuous passage between them. For I think that the 

 extremities of the arteries terminate in peculiar 

 vessels, which, soon after their origin, divide into an 

 almost infinite number of canals, or rather mem- 

 branous vesicles, joined here and there by various 

 anastomoses ; but that the various offshoots of these 

 vesicles, at last uniting into one canal, terminate in 

 the gaping mouths of the veins. So that, indeed, 

 while the mass of the blood wanders hither and 

 thither through' these tortuous labyrinths, it simulates 

 extravasation. Further, it is probable that those 

 passages, or the collection of the said vesicles, exist 

 separately in each fibre, for in vivisections a cut can 

 be made in the interstices of the fibres without any 

 flow of blood, while blood at once flows out when a 

 fleshy fibre is even slightly wounded. 



We may, then, conclude that that collection of 

 sanguiferous vesicles forms the chief part of muscular 

 flesh ; for as to the ruddy soHd part of the flesh, that 



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