108 



THE ESSENTIALS OF HISTOLOGY. 



they become easily detached. Next to this comes an elastic layer in 

 the form either of elastic networks (fig. 133) or of a fenestrated membrane 

 (fig. 132). In some arteries there is a layer of fine connective tissue 

 intervening between the epithelium and the fenestrated membrane (sub- 

 epithelial layer). 



FIG. 130. TRANSVERSE SECTION OF PART OF THE WALL OF THE POSTERIOR TIBIAL 

 ARTERY. (75 diameters.) 



a, epithelial and sub-epithelial layers of inner coat ; b, elastic layer (fenestrated membrane) 

 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. 



FIG. 131. EPITHELIAL LAYER LINING 

 THE POSTERIOR TIBIAL ARTERY. 

 (250 diameters.) 



Fig. 132. PORTION OF FENESTRA- 



TEU MEMBRANE OF HENLE FROM 

 AN 4RTERY. (Toldt.) 



The middle coat consists mainly of circularly disposed plain muscular 

 fibres, but it is also pervaded in most arteries by a network of elastic 

 fibres which are connected with the fenestrated membrane of the inner 

 coat and are sometimes almost as much developed as the muscular 

 tissue itself. This is especially the case with the larger arteries such 



