2gQ PHILOSOPHICAL TRANSACTIONS. [aNNO lOjQ. 



covered to be between veins and between arteries, in which vessels the blood 

 running with a large and rapid stream, should any of them chance to be ob- 

 structed, the circulation so necessary to life must needs be intercepted, without 

 some lateral conveyance of it into others of the same kind : which inconveni- 

 ence yet I supposed would hardly be alleged in thp present case ; that fabric of 

 those vessels seeming to be designed for extraordinary emergencies, but these 

 being according to the present supposition, the constant and necessary ducts of 

 this actuating matter. But nevertheless — ^Thirdly, It seemed difficult to solve 

 this intestinal contraction, though these lateral apertures were supposed : for if 

 fibres, whether considered as single or as constituting a muscle, be contracted 

 according to their length from some influent matter, it must be from a disten- 

 sion of them in breadth ; and, in order to that, this matter must undergo some 

 confinement in the part to be distended ; but if they have lateral perforations, 

 how c^n it be supposed that such a distension can happen, when the matter de- 

 signed to effect it has so ready a passage forth, especially its determination from 

 the impelling cause being in right lines downward? But indeed I think no 

 anatomists have observed, that muscles, supposing these such, receive their 

 actuating matter in at their sides, or, when their motion ceases, send it forth 

 that way ; but all so far as has been observed, are fenced with a considerably 

 compact and comparatively impervious membrane. — Fourthly, I considered that 

 all muscles are observed to have two tendons, one at each extremity, by the 

 approach of one whereof toward the other, its motion, which is contraction, is 

 performed ; but it seems hard to conceive, that these tendons should coincide, 

 as in this supposition they must, and if they do, I presumed it would be diffi- 

 cult to determine what part of these circular muscles the tendons are, and where 

 the motion should begin in each ; it being observed, that all muscles are 

 fastened to some, either simply or comparatively, immovable part, toward 

 \vhich they move, and by which the instinct of motion is from the nerves con- 

 veyed to them : but no anatomists having discovered that any one part of these 

 muscles, or moving fibres, whichsoever they be, has any stricter cohesion than 

 another with any of the adjacent parts, I conceived I might be allowed the liberty 

 to doubt of the hypothesis, especially if I could satisfy myself better by another. 

 For instead of those solutions, there occurred to me a third way, which seemed 

 more mechanically adjusted to solve the phenomenon, viz. That those fibres, 

 which have been esteemed annular, might perhaps be spiral, and so be con- 

 tinued down in one tract to the lowest extremity of the intestines : which if 

 true, it seemed probable to me, that when either a bare motion shall be im- 

 pressed on them at their beginning, or any substance impelled into them, the 

 motion must be successively continued all along their tracts, and must there- 



