280 GENERAL ANATOMY. 



kled in the retracted arteries after amputation. Its inner sur- 

 face is smooth, polished, moist, and in contact with the blood; 

 its outer surface adheres to the middle membrane. In the 

 arterial trunk, it can be divided into several layers. The in- 

 nermost is extremely thin, and transparent; the others are of 

 an opaque white, and passes insensibly into the middle mem- 

 brane; it is to this part especially, that the name of nervous 

 membrane has been given. In the branches, it forms only a 

 single indivisible lamina. No appearance of fibres is distin- 

 guished in this membrane, which is very dense ; it tears nearly 

 with the same facility in all directions. It has little elasticity. 

 It has been compared to the serous membrane and the mucous 

 or cellular tissue. It is not vascular like the serous membrane 

 generally; and it is to the arachnoid membrane that it bears 

 the greatest resemblance. 



413. Cellular tissue, vessels and nerves, also enter into 

 the composition of the arteries. 



The cellular tissue which penetrates into the outer mem- 

 brane, and which unites it to the middle one, is sufficiently 

 apparent, but beyond this, it is so rare and compact, that its 

 existence has been doubted. However, when by dissection 

 the outer membrane, and the greater part of the thickness of 

 the middle one are removed from an artery, there spring from 

 the uncovered part fleshy granulations, as from the remainder 

 of the wound. 



414. The arteries and veins of the arteries (vctsa artcria- 

 rum 9 ) are furnished by the neighbouring vessels, and become 

 very apparent in the outer membrane by injections, and even 

 sometimes without them, particularly in young subjects. They 

 have been traced to their entrance into the middle membrane, 

 but no farther. 



What are called exhalent and absorbent vessels, or more 

 correctly the unknown passages of exhalation and inhalation, 

 are demonstrated iti the parietes of the arteries by the fact 

 itself, for in inflammation of the arteries an exhalation occurs 

 at their internal surface; and, in cases of ligatures, the internal 

 coagulum is absorbed. 



