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elastic fibres, with a certain proportion of areolar tissue. In the larger 

 arteries (Fig. 110) its thickness is comparatively as well as absolutely 

 much greater than in the small, constituting, as it does, the greater part 

 of the arterial wall. 



The muscular fibres, which are of the unstriped variety (Fig. 109) are 

 -arranged for the most part transversely to the long axis of the artery 

 (Fig. 107, m); while the elastic element, taking also a transverse direc- 

 tion, is disposed in the form of closely interwoven and branching fibres, 

 which intersect in all parts the layers of muscular fibre. In arteries of 



FIG. 109. 



FIG. 110. 



FIG. 109. Muscular fibre-cells from human arteries, magnified 350 diameters. (Kolliker.) a. 

 Nucleus, b. A fibre-cell treated with acetic acid. 



FIG. 110. Transverse section of aorta through internal and about half the middle coat. a. Lin- 

 ing eudothelium with the nuclei of the cells only shown. 6. Subepithelial layer of connective tissue. 

 c, d. Elastic tunica intima proper, with fibrils running circularly or longitudinally. e,f. Middle coat. 

 consisting of elastic fibres arranged longitudinally, with muscle-fibres cut obliquely, or longitudinally. 

 (Klein.) 



various size there is a difference in the proportion of the muscular and 

 elastic element, elastic tissue preponderating in the largest arteries, while 

 this condition is reversed in those of medium and small size. 



The internal coat is formed by layers of elastic tissue, consisting in 

 part of coarse longitudinal branching fibres, and in part of a very thin 

 and brittle membrane which possesses little elasticity, and is thrown into 

 folds or wrinkles when the artery contracts. This latter membrane, 

 the striated or fenestrated coat of Henle (Fig. 108), is peculiar in its ten- 

 dency to curl up, when peeled off from the artery, and in the perforated 



