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cent cellular substance, but its internal face is united more close- 

 ly to the middle coat; not, however, so tightly as to prevent a 

 slight sliding of the one upon the other, and to forbid their easy 

 separation by a knife. Scarpa is not disposed to admit this as 

 one of the coats of arteries, and says that it only serves as an 

 exterior envelope, and retains them in their places. This coat 

 manifests its fibrous character in not being dis-posed to secrete 

 fat, and is more distinct in the large arterial trunks. It has con- 

 siderable strength and elasticity, both circularly and longitudi- 

 nally, and is remarkable for its whiteness. If an artery be sur- 

 rounded by a tightly drawn ligature, the middle and the inter- 

 nal coats will be completely cut through by it, while the exter- 

 nal coat remains entire. This coat, then, answers the purpose 

 of a strong investing fascia,* in which respect it may be consi- 

 dered as a sheath to the proper arterial structure, though the 

 term sheath is commonly applied to the cellular membrane on 

 its outer side. 



The Middle Coat of the arteries is called the Muscular, the 

 Proper, the Tendinous, and so on. It is of a light yellowish 

 tinge, and decreases continually in thickness, with but few ex- 

 ceptions, from the heart to the ends of the arteries ; it is, how- 

 ever proportionately thicker in the small arteries than in the 

 large ones. Its fibres are circular, but do not individually per- 

 form the circuit of the vessel. They are parallel to each other, 

 and adhere laterally by very slender ties. In the larger arte- 

 ries, this coat may be divided into several laminae, though the 

 division is entirely artificial. There are no longitudinal fibres 

 whatever in it; the consequence of which is, that an artery di- 

 vested of its external coat, yields more readily in the direction 

 of its length than of its circumference. 



The middle coat has a firmness, whereby, even when an ar- 

 tery is emptied, the cylindrical shape is still retained. Its cha- 

 racter seems to be the result of a mixture of elastic and of 

 muscular properties derived fron a state of tissue entirely pe- 

 culiar; but which some anatomists have been very desirous of 

 ranging under the head of muscles, others under that of liga- 

 ments, and a third, under both united. The celebrated John 



* Jones on Hemorrhage* 



