274 THE BLOODVESSELS, BY C. J. EBERTH. 



teric, the splenic, and renal arteries of oxen, but in the sheep 

 they are scarcely perceptible in the arteria mesenterica. In 

 both, the bundles are collected into a thick uninterrupted 

 longitudinal layer. 



I was only able to find internal longitudinal muscles in the 

 form of isolated cells in the internal longitudinal fibrous tunic 

 of the hepatic, splenic, and crural arteries. I was not able to 

 discover them in the remaining abdominal vessels, nor in the 

 axillary and popliteal arteries, where Kblliker believed he had 

 recognised them. 



A delicate layer, composed of contractile longitudinal fibres, 

 exists, according to Kemak, in the internal longitudinal fibrous 

 tunic of the renal, splenic, hepatic, and mesenteric arteries of 

 man, the ox, sheep, and pig. These muscles, however, are 

 only found near the origins of these vessels, and on the proxi- 

 mal side of the point at which the branches are given off 

 from the trunk. In oxen, these muscles form thick, strongly 

 projecting longitudinal cords that are crossed by strong circu- 

 lar fibres near the larger openings, and there constitute a 

 kind of sphincter. 



Through these longitudinal muscles the openings of the less 

 fixed vessels, given off at acute angles, are probably kept con- 

 tracted when, in consequence of the strong contraction of the 

 discharging vessels, the passage of the blood is checked. This 

 longitudinal fibre layer is absent in those vessels where, on 

 account of their fixity, and the equality of the strength of the 

 blood column, this provision is not required, as in the inno- 

 minate, carotid, and subclavian arteries. 



I have observed scattered longitudinal muscles in the tunica 

 interna, at the points where branches are given off at acute 

 angles, as at the division of the external iliac into the femoral 

 and profunda arteries. 



Distinct external and internal longitudinal muscles are only 

 found in the extremely muscular umbilical arteries. The cir- 

 cular muscular layer is here lined internally by a continuous 

 layer of longitudinal muscles, and externally by interrupted 

 and slender muscular bundles, running in the same direction. 



EXTERNAL ELASTIC COAT, AND TUNICA ADVENTITIA. The 



