THE CIRCULATION OF THE BLOOD. 



107 



(c) The internal coal 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 



j 



FIG. 99. Transverse section of aorta through internal and about half the middle coat. a. Lining 

 endothelium 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 muscular fibres, cut obliquely or longitu- 

 dinally. (Klein.) 



into folds or wrinkles when the artery contracts. This latter mem- 

 brane, the striated or fenestrated coat of Henle (Fig. 97), is peculiar in 



FIG. 100. Transverse section of small artery from soft palate, e, endothelial lining, the nuclei 

 of the cells are shown ; t, elastic tissue of the intima. which is a goo.t deal folded ; c, m, circular 

 muscular coat, showing nuclei of the muscle cells ; t.a, tunica adventitia. X 300. (Schofleld.) 



its tendency to curl up, when peeled off from the artery, and in the per- 

 forated and streaked appearance which it presents under the microscope. 

 Its inner surface is lined with a delicate layer of elongated endothelial 



