270 THE BLOODVESSELS, BY C. J. EBERTH. 



of doubt whether they are to be regarded as normal or patho- 

 logical constituents. In some instances, the nuclei of the 

 fusiform cells present so well marked a rod-like form as to 

 lead to the supposition that smooth muscles are present. But, 

 like Kblliker,* who first drew attention to them in the axillary 

 and popliteal arteries, I have been unable to convince myself 

 of the presence of smooth muscles in the internal coat of these 

 vessels. On the other hand, I have met with isolated muscle 

 cells in the internal longitudinal fibrous tunic in the hepatic 

 and splenic arteries, and in the crural, at the points where they 

 divide. 



COAT. The transition of a capillary into an 

 arterial tube commences with the appearance of scattered 

 transversely disposed fusiform muscle cells, immediately exter- 

 nal to the endothelial tube, and between it and the tunica 

 adventitia. 



The muscle cells, which at first form only a single interrupted 

 layer, gradually increase in number, and come to constitute an 

 independent layer of cells, adjoining to and superimposed 

 upon each other. Externally, this layer is, for the most part, 

 sharply bounded by the external elastic tunic, or by the 

 tunica adventitia, and internally by the inner elastic membrane. 



I find that a short portion of the pulmonary artery and the 

 aorta, immediately above the attachment of the semi-lunar 

 valves, are destitute of muscle. 



Many arteries possess no muscles whatever. Leydig f found none 

 in tjie . aorta of Balaena musculus, nor in the aorta and other larger 

 arteries of Raja batis, Spinax niger, and Polypterus, nor in the 

 basilar artery of the brain of Scymnus lichia, the fine cerebral ar- 

 teries of which, however, contain distinct circularly arranged muscles. 



With the exception of the largest arterial trunks, the mus- 

 cular layers consist of finely granular connective tissue, con- 

 taining scattered cells, and traversed by a few fine elastic 

 fibrils, in which lie a number of muscle cells, more or less 



* Zeitschrift fur wissenschaftliche Zoo/o^e,Band i., p. 81, 1849. 

 t Lehrbuch, 1857. 



