CYCLOP ^D I A: ^^ 



OR, A NEW 



UNIVERSAL DICTIONARY 



OF 



ARTS and SCIENCES. 



ART 



ARTERY, in ^Ha/«OT_)', from a»if, (7;V, and TiifEi', /o yfff/i, denfed cellular fubflance ; it is powerfully elaftic, and 



is the name by which thofe vcffels are diftinguiftied abounds in the larger arteries, but gradually diminilhes 



through which the blood flows from the heart to in quantity as the fize of the veflel decreafes; fo that the 



every part of the body. The term was firft adopted by the fmall arteries are quite flaccid, and coUapfe when divided, 



anatomifts of the Alexandrian fchool, in confequence of It is eafy to perceive the ufe of thefe various degrees of 



the enontous opinion which they entertained, that thefe elafticity and mufcular po)\-er, which are given to the dif- 



vefliels were defigned for the diilribution of air throughout ferent fets of arteries. In the large arteries, mufcular 



the body. power feems unneceffary, for the ferce of the heart is 



Arteries, Slnidtire of. The larger arteries have thick fully adequate to the propulfion of the blood; but in the 



and elaftic fides, fo that they remain open when divided, and fmaller arteries, where the effetl of the heart's aftion de- 



prefcnt a regularly circular aperture. The fides may be 

 feparated into th-. ee flrata of diflimilar fubftances, which are 

 technically called coats. The innermol^, whicli is generally 

 termed the cuticular coat, is very thin, but very ftrong and 

 inelaftic. Upon this circumflance depends the regularly 



clines, a proportionate mufcular power is allotted to the 

 veflel to urge on the circulating fluids. The arteries hae 

 their nutrient arteries and veins, their abforbents, and their 

 nerves. All the arteries proceed from one great veflel, as 

 the branches fpring from the trunk of the tree; and we 



circular form of an injected artery ; for if the cuticular coat proceed to notice certain circumftances obfervable in 



burfts from too great force being ufed in injefting, the ex- Arteries, the Ramification of the. i. When a large 



terior elallic coats are diftended into an irregular and uncer- artery gives off a branch, the conjoined areas of the two 



tain figure. The internal furface of this coat is perfectly veflels make a greater fpace for the blood to move in, 



fmooth, fo that the blood ghdes along it without impedi- than the area of the original veflel. The increafe of 



ment ; the external furface is a little rough, and is conne&ed dimenfions in the branches of a large artery is flight, 



by cellular fubflance to that coat which furrounds it. The but in thofe of a fmall one it is fo confiderable, that 



middle or mufcular coat coufifts of circular fibres which are Haller has cflimated it as fui-paffing by ^d that of the 



fcarcely yifible in the largeft; arteries, but are verj- manifell trunk from which they fprung. The conjoined areas of 



and ftrong in the fmaller ones ; they are feen projetling in all the fmall arteries fo greatly exceed that of the aorta, 



circular ridges, beneath the thin cuticular coat of a fmall that the fame anatomilt, in oppofition to former opinions, 



artery, when it is flit open. Tlie great increafe of the muf- fays, thefe veffels may be confidered as conical, the bafis of 



cular power of the fmall arteries is not only evident to the the cone being in the extreme arteries, and the apex in the 



fight, but has been demonftrated by experiment. Mr. 

 Hunter bled a horfc to death, and afterwards examined the 

 ftate of the arteries. The aorta was contraiSed about ■j^th 

 part of its natural area, the iliac ^th, the radial \. See his 

 Treatife on the Blood, Inflammation, fee. The external 



heart. 



2. '\^^Jen a large artery fends off a branch, its courfe does 

 not, in general, deviate further from that of the trunk, than 

 an angle of 45 degrew. Sometimes a branch, whicli lias 

 gone off^ at an acute angle, returns, and proceeds in a Con- 

 or elaftic coat of the arteiy appears to be made of con- trary direilion to that of the trunk ; and thefe arteries are 

 Vol. III. H generally 



444044 



