STRUCTURE OF ARTERIES. 



clxix 



Fig- XCI. 



be stripped off in large pieces. It is very commonly corrugated with very 



fine and close longitudinal wrinkles, caused most probably by a contracted 



state of the artery after death. Such is the appearance presented by the 



internal coat to the naked eye, but by the aid of the microscope it Ls found 



to consist of two different structures, namely: 1. An epithelium, forming 



the innermost part or lining. This is a simple layer of thin elliptical or 



irregularly polygonal scales, which are often elongated into a lanceolate 



shape. These epithelial elements have round or oval nuclei, which, how- 



ever, may disappear ; indeed, the whole structure sometimes becomes indis- 



tinct, especially in the larger arteries. 2. Elastic layers. These form the 



chief substance of the inner coat. The elastic tissue appears for the most 



part in form of the "perforated" or " fenestrated " membrane of Henle. 



This consists of a thin and brittle transparent film, and may exist in one 



or several layers ; and in that case it may be stripped off in small shreds, 



which have a remarkable tendency to curl in at their upper and lower 



borders, and roll themselves up as represented in the figure (fig. XCI.). 



The films of membrane are marked by 



very fine pale streaks, following prin- 



cipally a longitudinal direction, and 



joining each other obliquely in a sort 



of network. Henle considers these 



lines to be reticulating fibres formed 



upon the membranous layer. This mem- 



brane is further remarkable by being 



perforated with numerous round, oval, 



or irregularly shaped apertures of dif- 



ferent sizes. In some parts of the arte- 



ries the perforated membrane is very 



thin, and therefore difficult to strip off ; 



in other situations it is of considerable 



thickness, consisting of several layers ; 



but it often happens that the deeper 



layers of the elastic structure, i. ,, those 



farther from the inner surface, lose their 



membranous character, and pass into a 



mere network of longitudinal anasto- 



mosing fibres of elastic tissue. These 



longitudinal reticulating fibres are, however, sometimes spoken of as consti- 



tuting a distinct coat. 



The inner coat may thus be said to be formed of epithelium and elastic 

 layers ; the latter consisting of elastic tissue under two principal forms, 

 namely, the fenestrated membrane and the longitudinal elastic networks : 

 and these two forms may coexist in equal amount, or one may predominate, 

 the other diminishing or even disappearing altogether. 



It is further to be observed, that in the inner coat of the aorta and the larger 

 arteries, in addition to the elements described, lamellae are found of a clear, homoge- 

 neous, often striated or sometimes even fibrillated substance, mostly of the nature of 

 connective tissue, and pervaded by longitudinal elastic networks of varying fine- 

 ness. Immediately beneath the epithelium these transparent layers, the striated 

 layers (Kolliker), may contain imbedded nuclei, which have been found by 

 Langhans to belong to branched or irregularly stellate cells ; or they may be more 

 uniform and destitute of nuclei, in which case they more resemble elastic mem- 

 branes. 



TEIVT, MAGNIFIED 200 DIAMETERS (from 

 Henle). 



a , b, c, perforations. 



