. Quain's elements of anatomy . and retractile both in then- length and theirwddth. When cut across they jjresent, although empty, an open orifice ;the veins, on the other hand, collapse, unless when prevented by connec-tion with surrounding rigid joarts. Structure.—In most parts of the body the arteries ai-e inclosed ina sheath formed of connective tissue, and their outer coat is connectedto the sheath by filaments of the same tissue, but so loosely that, whenthe vessel is cut across, its ends readily shrink some way within thesheath. Some arteries want sheaths, as those for example which are
. Quain's elements of anatomy . and retractile both in then- length and theirwddth. When cut across they jjresent, although empty, an open orifice ;the veins, on the other hand, collapse, unless when prevented by connec-tion with surrounding rigid joarts. Structure.—In most parts of the body the arteries ai-e inclosed ina sheath formed of connective tissue, and their outer coat is connectedto the sheath by filaments of the same tissue, but so loosely that, whenthe vessel is cut across, its ends readily shrink some way within thesheath. Some arteries want sheaths, as those for example which aresituated within the cavity of the cranium. Independently of this sheath, arteries (except those of minute sizewhose structure will be afterwards noticed with that of the capillaries) STEUCTURE OF AETEEIES. 185 liave been usually described as formed of three coats, named, from theirrelative position, internal, middle, and external (fig. 178, in section) ;and ■ as this nomenclatme is generally followed in medical and surgical. Fig. 17S.—Transverse sectiox of part of the wall of the posterior tibial ARTEIir (man). 75 DIAMETERS. () a, Epithelial and subepithelial layers of inner coat; h, elastic layer (fenestrated mem-brane) of inner coat, appearing as a bright line in section; c, muscular layer (middlecoat) ; d, outer coat, consisting of connective tissue bundles. In the interstices of thebundles are some connective tissue nuclei, and, especially near the muscular coat, a numberof elastic fibres cut across. ■works, and also correctly applies to the structure of arteries so far as it isdiscernible by the naked eye, it seems best to adheTe to it as the basis ofour description ; although it wiU be seen, as we proceed, that some ofthese coats are found on microscopic examination really to consist of twoor more strata differing from each other in textme, and therefore reckonedas so many distinct coats by some authorities. Internal coat {Tunica iiitma) (fig. 178, a, b).Thi
Size: 2371px × 1054px
Photo credit: © Reading Room 2020 / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., boo, bookcentury1800, booksubjectanatomy, booksubjecthumananatomy
