. Elementary physiology . Fig. 57.—Transverse section of part of the wall of the posterior tibial artery. (75 diameters.) a, epithelial and subepithelial layers of inner coat; b, elastic layer (fenestrated mem- brane) of inner coat, appearing as a bright line in section ; c, muscular layer (middle coat); d, outer coat, consisting of connective-tissue bundles. In the interstices of the bundles are some connective-tissue nuclei, and, especially near the muscular coat, a number of elastic fibres cut across. there appears in addition an external coat {areolar coat or timica adventitia) composed of
. Elementary physiology . Fig. 57.—Transverse section of part of the wall of the posterior tibial artery. (75 diameters.) a, epithelial and subepithelial layers of inner coat; b, elastic layer (fenestrated mem- brane) of inner coat, appearing as a bright line in section ; c, muscular layer (middle coat); d, outer coat, consisting of connective-tissue bundles. In the interstices of the bundles are some connective-tissue nuclei, and, especially near the muscular coat, a number of elastic fibres cut across. there appears in addition an external coat {areolar coat or timica adventitia) composed of connective-tissue fibres. Many of these fibres are elastic; especially in the arteries which require more elastic distensibility than the veins. It is this external coat which gives their great strength to the large vessels, and especially to the arteries in which it is well developed. In the very largest arteries, such as the aorta and its pfimary branches, the middle or muscular coat and the outer coat become to a certain extent blended so that there is an admixture of elastic and muscular fibres. In a typical medium-sized artery (see Fig. 57) the wall is ^ The purpose of this muscular coat in the arterioles, and the manner in which it regulates the supply of blood to a given part, have already been described (see pp. 57, 60).
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Keywords: ., bookcentury1800, bookdecade1890, bookpubli, booksubjectphysiology
