678 SPECIAL HISTOLOGY. 



the vertebral canal, the vence cavce, the jugular, iliac, and crural veins, 

 and in those of the liver by myself. They are derived both from the 

 sympathetic and the spinal nerves, and with regard to their termina- 

 tions have not yet been investigated. According to Luschka, they 

 would appear to extend to the innermost vascular tunic ; but this I have 

 not as yet been successful in observing. 



§ 215. For more easy description, the arteries may be divided, ac- 

 cording as the middle tunic is purely muscular, or composed of muscu- 

 lar and clastic fibres intermixed, or else chiefly elastic, into small, 

 medium sized and large arteries ; and the more properly so, because, 

 concomitantly with the variations in the structure of the middle tunic, 

 the external and internal coats present a different conformation, at all 

 events, in many respects. A general characteristic of the arteries is 

 presented in the circumstance, that the middle tunic is very strong, and 

 consists of numerous, regularly disposed lamince, the elements of which 

 observe a transverse direction. In the largest arteries the t. media is 

 yellow, highly elastic, and of great thickness ; towards the periphery of 

 the body it gradually diminishes in thickness, and becomes redder and 

 more contractile, until, just before the capillaries are reached, it appears 

 quite thin and subsequently inapparent. The whitish t. intima is 

 always much thinner, and varies in thickness within narrower limits, 

 but this is also regulated by the size of the vessel ; whilst, on the con- 

 trary, the t. adventitia of the largest arteries is absolutely considerably 

 thinner than in those of a medium calibre, in which it often equals the 

 t. media in thickness, or may even exceed it. In a special exposition 

 of these points, it is best to begin with the smallest arteries as the 

 simplest in structure ; with these the others may be afterwards readily 

 compared. 



Arteries under 4-5 or 1 line in diameter, with few exceptions, present, 

 until close to the capillaries, the following structure (Fig. 279). The t. 

 intima consists of only two lamince, an epithelium., and a peculiar, glis- 

 tening, less transparent membrane, wdiich I shall term the elastic inter- 

 nal tunic. The former contains well-marked, fusiform, pale cells with 

 long-oval nuclei, Avhich are readily separated in connection, in entire 

 fragments, or even in the form of perfect tubes ; but may also be iso- 

 lated, and then present no small resemblance, on the one hand, with the 

 fusiform cells of pathologists (also with the formative cells of the elastic 

 fibres and of connective tissue), and on the other with contractile fibre- 

 cells ; from the former, however, they are distinguished by the less atte- 

 nuation of their extremities and their paleness ; and from the latter by 

 their rigidity, by the nuclei never having the rod-like form, and by their 

 chemical reactions. The elastic tunic is, on the mean 0-001 of a line 



