

PERIPHERIC ORGANS OF THE CIRCULATION. 153 



indicates that they have a natural form, to which they are con- 

 stantly tending to return, and which is antagonized by the force 

 of the circulation. Moreover, they are not, as we should be 

 likely to suppose, hollow cylinders, but rather hollow ribbons, 

 with flattened sides. An artery of middle size contains muscu- 

 lar and elastic tissue in about equal parts. If there were only 

 muscular tissue in the arteries, as this is arranged in circular 

 layers like a sphincter, the whole central opening in the 

 artery, on assuming its natural form of repose, would be a 

 point or axial line, serving only as an indication of the canal 

 (Fig. 48, A). The elastic tissue has a tendency to keep the 

 artery wide open, and, if this alone existed, it would have the 

 appearance of a large cylindrical canal (B). By a sort of 

 compromise this constant antagonism between the elasticity 

 of the muscle and the elastic tissue produces an intermediate 

 form between these two extremes, that of a cylindrical, flat- 

 tened ribbon (C, or rather D) slit transversely. 1 



This natural form is constantly opposed by the mass of 

 blood which the ventricle at each systole causes to gush into 

 the arterial system ; the arteries, when full of blood, have 

 also the form of a cylindrical tube ; but we know, too, that 

 they change their form according to the greater or smaller 

 quantity of blood which they receive. In cases of severe 

 hemorrhage, they assume their natural ribbon-like form ; 

 they assume it also, after death, by ejecting their contents 

 into the capillaries and the veins ; thus th arteries of a dead 

 body are empty and flat. We must, however, add, that they 

 preserve this form in the dead body, only when the air has 

 not entered their interior. Directly any opening is made in 

 their coats, they begin to draw in the air, and to assume the 

 appearance of hollow cylinders. This fact is easily explained : 

 after the last pulsation of the heart, the arteries still endowed 

 with their vital activity have, by ejecting their content into 

 the veins, taken the natural form of a hollow, flattened rib- 

 bon, which form is due to the antagonism between the muscu- 

 lar and elastic tissue; the muscular tissue, however, soon loses 

 its properties, and from that moment, in a physiological point 

 of view, the artery is composed only of elastic tissue, the 

 natural form of the artery of a dead body being consequently 



1 See Louis Oger, " Considerations Physiologiques sur la Forme 

 Naturelle et la Forme Apparente de quelques Organes, et en particulier 

 sur la Forme Naturelle et la Forme Apparente des Arteres." These 

 de Strasbourg, 1S70, No. 2S<3. 



