Anatomy of the Umbilical Cord. 433 



IV. Its Vessels. 



In all previous descriptions it seems to have been taken for granted 

 that the umbilical vein and arteries are identical with blood-vessels else- 

 where ; but I have already pointed out some important differences, and 

 I have now to describe some others. 



"When the arteries and vein of a cord which has been removed from 

 a mature and liviug child are examined, the arteries are found con- 

 tracted to a very small size, and the vein is also found to be much con- 

 tracted. The introduction of a tapering probe into the canal of an 

 artery or of a vein shows that it can be readily dilated ; and the forcible 

 distention of the whole tube with water may be made to enlarge the 

 diameter of the tube as much as four or five times. In the vein the 

 possible distention is even greater ; but in both there is a limit to it, and 

 the walls are so strong that they resist a pressure of 800 millims. The 

 distention is quite equable, and never presents any sacculations. 



The proper tissue of the vessel is made up of the ordinary fusiform 

 fibre-cells with their characteristic rod-shaped oval nuclei, the external 

 coat being, as I have already shown, the canalicular tissue of the district 

 proper to each blood-vessel. To the arteries there is certainly no inner 

 or endothelial coat, though when the vessel is coutracted, the inner fibres 

 being pressed into folds by the contractions of the outer layers, their 

 nuclei present at the apex of the fold a very deceptive appearance (Plate 14. 

 fig. 25). Staining with silver or hematoxylin, however, gives the most 

 decided indications of the absence of endothelium in the arteries, but in 

 the vein it is probably present. 



When a section is made of a fresh cord, removed from a mature and 

 living child, in which one artery has been distended and the other left 

 untouched, it will be seen that the contraction produces an arrangement 

 of folds somewhat resembling what takes place in the closure of the 

 oesophagus. The inner layers contract ; but the outer layers seem to 

 contract still more, so that the internal fibres become bent on themselves 

 and form rugose prominences, which almost meet in the middle of the 

 lumen of the tube (Plate 13. fig. 20) In the vein the muscular wall is 

 much thinner, and this folding of the inner walls is not seen. 



This does not take place in any other artery which I have examined 

 for the purpose; at least, if it does so it becomes undone after death; but 

 I did not find it in the carotid of a guineapig divided and examined 

 immediately after death. 



This extraordinary power of contraction of the umbilical artery is due 

 to three conditions — the exceptional thickness of the muscular layer, the 

 absence of any restraint by a firm external or any internal coat, and a 

 peculiar arrangement of the external bundles of muscular fibres. 



In the distended artery, examined after the addition of acetic acid, or 

 after treatment by hematoxylin or silver lactate, the rod- shaped nuclei 

 are seen to lie all in parallel directions, which are concentric with the 



