300 GENERAL ANATOMY. 



of those of the uterus, the liver, &c. which are attached to the 

 suhstance of the organs. They are less extensible in the lon- 

 gitudinal direction than the arteries, but much more so in the 

 circular. Since Wintringham's experiments, it is generally 

 admitted that the veins oppose a much greater force to the 

 causes of rupture than the arteries; on the other hand, they 

 not only yield much more to distention, but also tear across, 

 much more frequently than the arteries, while, on the con- 

 trary, they have appeared to me to resist greater distention 

 longitudinally. The parietes of the veins are very elastic, 

 but less so than those of the arteries. Their irritability or 

 vital contractility is, on the contrary, greater than that of the 

 arteries, but less than that of the capillaries. It has been de- 

 nied by several physiologists, but proved by many experi- 

 ments. It is sufficient to have observed the effect of local 

 cold on the subcutaneous veins, and to know that the portion 

 of a vein between two ligatures, when punctured, empties it- 

 self entirely and rapidly in a living animal, while this does 

 not occur after death, to admit the existence of irritability in 

 the veins. Their sensibility is obscure or doubtful; Monro, 

 in his lectures, affirmed that he had felt the puncture of a de- 

 nuded vein. The force of formation of the veins is not less 

 evident than that of the arteries. 



449. The function of the veins is to convey the blood 

 from every part of the body to the heart. We have seen that 

 each contraction of the ventricles determines an augmentation 

 of the continuous movement of the blood in the arteries; this 

 augmentation goes on diminishing in the same degree as the 

 vessels become capillary. In these latter, as well as in the 

 veins generally, the movement is uniform. The blood in the 

 veins is animated by the movement imparted to it by the 

 heart, the arteries, and by the capillary vessels. Do the veins 

 exercise an additional action? This is not doubtful; let any 

 one compress or tie the artery of a member in an animal, the 

 flow of the blood in the veins will be slower; but will not be 

 for this stopped; if a vein be tied, it will however empty itself 

 above the ligature, it empties itself even between two liga- 

 tures. To the causes already mentioned, we must add the 



