224 



ARTERY. 



they are more numerous and larger in young sislance in either direction. The middle and 



than in adult and old subjects. internal tunics are as remarkable for their fra- 



Absorbents are not visible on the coats of gility as the external is for its toughness and 



any arteries except the larger trunks; however, great power of resistance ; hence it is, that when 



a 



ligature 



is tightened on an artery, the two 

 former are divided, while the latter remains 

 unbroken, as proved by the experiments of 



Dr. Jones.* 



The successful employment of torsion of the 



the removal of coagula formed in the interior 

 of all arteries after the application of ligatures 

 may be regarded as proving the existence of 

 absorbents in every part of the arterial system. 

 The arteries are plentifully supplied with 



nerves, of which the aortic system receives more arteries as a means of suppressing haemorrhage 

 in proportion than the pulmonary artery, and is in like manner owing to the greater power of 



the smaller arteries more than the larger trunks, resistance possessed by the external tunic as 

 The trunk of the aorta, the pulmonary artery, compared with the other two. The process by 



and the arteries of the head, neck, thorax, ab- which arteries are obliterated by torsion is thus 



domen, and those of the genital organs, receive explained by M. Arnussat,f to whom belongs the 



their supply from the nerves of organic life, merit of having been the first to propose and 



These form a very intricate plexus on their practise it. The divided extremity of an artery 



surface. The arteries of the extremities receive is seized between the blades of a forceps, and 



their supply of nerves from those of animal drawn out beyond the surface of the wound : 



life in their neighbourhood. Two sets of nerves the vessel is then taken hold of with a second 



have been described as being furnished to the pair of forceps a few lines higher, and held 



arteries; one set, consisting of softer nerves, of firmly while the operator commences to twist 



a flattened form, are said to be lost in the eel- the forceps with which he holds the extremity 



lular or external tunic, nervi molles ; the other of the vessel in the direction of its axis, making 



set, more firm and round, penetrate the middle from five to nine or ten turns, according to the 



tunic, in which they form a thin membraniform size of the vessel operated upon. On examin- 



expansion, containing distinct fibres. Meckel* ing an artery which has undergone this process, 



justly considers the internal nerves as subdivi- it will be found that the middle and internal 



sions of the larger flattened external branches, tunics of the twisted portion have been broken 



No nerves have yet been discovered on the in several places by the external tunic, which, 



umbilical arteries, and the arteries of the brain remaining unbroken, is formed by the twisting 



are supposed to be without any. The nerves process into a sort of spiral ligature, so tightly 



of the arteries become less apparent in old age. applied round the inner tunics as to set at 



The specific gravity of the arteries exceeds defiance every attempt to unravel it by twisting 



that of distilled water in the proportion of the vessel in the opposite direction. 

 106 to 100. They are proportionally lighter The arteries are highly elastic ; they admit of 



and less dense than the veins ; while the veins considerable distension in the longitudinal di- 



possess more power of resistance, and are not rection, and quickly contract to their original 



so easily ruptured as the arteries. length on the cessation of the distending force. 



Physical properties, Of the physical pro- In the transverse direction they yield less, and 



perties of the arteries the most remarkable are after distension resume their previous state with 



the firmness of their parietes, their power of greater force. When a fluid is injected with 



resistance, and their elasticity. It is owing some force into the arteries in the dead body, 



to the firmness, which principally resides in they become distended and elongated ; and if, 



their middle tunic, that they preserve their when they are in this state, the force with 



circular form in the empty state. which the injection was propelled be removed, 



Their power of resistance has been made the they will contract to their previous state, or 



subject of experiment by Wintringham,f and, nearly so, expelling a portion of the fluid which 





more recently, by Beclard,^ from which the 

 following results have been obtained. 



Their power of resisting rupture is very great, 

 and is generally in proportion to their thickness, 



had been thrown into them. During life the 

 arteries are in a state of elastic tension, so that, 

 when divided, their cut extremities retract with- 

 in their sheath. 



being greater in the aorta than in the pulmonary The arteries are endowed with the power of 

 artery. As the arteries diminish in size, their contracting in a gradual manner, which they 

 absolute resistance diminishes; however, as their exhibit under the following circumstances: 

 relative thickness and softness increase, their when the passage of the blood is stopped in the 

 extensibility and relative resistance undergo a principal artery of a limb, the vessel gradually 

 proportionate augmentation. The resistance of 

 all arteries of equal volume is not the same : 

 for instance, that of the iliac artery is greater 

 than that of the carotid. It is in the external 

 tunic that the power of resistance in the longi- 

 tudinal direction resides ; the resistance in the 

 circular direction is much greater, arid is owing 

 to the middle and external tunics conjointly; 

 the internal tunic has very little power of re- 



> Op. cit. 



t Experimental Inquiry on some 

 Animal Structure. Lond. 1740. 

 Anatomie Gencrale, p. 373. 



parts of the 



contracts, its cavity is reduced in size, and 

 ultimately becomes obliterated by degenerating 

 into a filamentous band of cellular tissue ; while 

 the collateral branches, taking up its function 

 of conveying blood to the distant parts, are 

 proportionally enlarged, rendered more tortuous, 

 and increased in length. In process of time 

 the number of enlarged collateral branches 

 diminishes, and one or more vessels of in- 

 creased size become as it were promoted to 



* Treatise on Haemorrhage. Lond. 1805, 

 t Archives Generales de Mdecine, t. xx. Aout, 

 1829, p. 606. 



