4 86 



STRUCTUEE OF SMALL ARTERIES. [sect. 2 1 4. 



thickness is often equal to that of the middle coat, or may even be 

 greater. In the more detailed account of the vessels, it will be 

 best to commence with the smallest arteries, as being simplest in 

 structure, upon which the others will readily follow. 



Arteries below four-fifths of a line or a line in diameter, present, 

 with few exceptions, the following structure, till near to the capil- 

 laries (fig. 197). The tunica intima consists of two layers only, an 

 epithelium and a peculiar shining, less transparent membrane, which 

 I will call elastic inner coat. The former has well-marked fusiform 



Fig. 197. 



An artery from the mesentery ot a child, (V0G2'", and vein, &, 0'067'" In 

 diameter, treated with acetic acid, and magnified 350 times, a. tunica ad- 

 ventitia, with elongated nuclei ; /3. nuclei of the contractile fibre-cells cf the 

 tunica media, seen partly from the surface, partly apparently in transverse 

 section ; 7. nuclei of the epithelial cells ; 5. elastic longitudinal fibrous coat. 



pale cells, with oval nuclei disposed longitudinally : groups of 

 these can be extremely easily isolated, in entire shreds, or even as 

 complete tubes, but the cells may also be demonstrated separately, 

 and they then possess no slight resemblance to the fusiform cells 

 of pathologists (also to the formative cells of elastic fibres and con- 

 nective tissue) ; and, on the other hand, they much resemble the 

 contractile fibre-cells : from the former of these, however, they are 

 distinguished by their less pointed ends, and by their paleness, and 

 from the latter by their stiffness, by the non-cylindrical nuclei, 

 and by their chemical reactions. The elastic inner coat is, on an 

 average, o-ooi"' thick, and is smoothly stretched out during life 

 under the epithelium ; but when the artery is empty, it almost 



