128 LECTURE Y. 



ordinary great contractility of the umbilical vessels, 

 which can be so readily seen in action on a large scale 

 when mechanical stimuli are applied, when the vessels 

 are divided with scissors or are pinched, or after the 

 employment of electrical stimuli. Sometimes, upon the 

 application of external stimuli, they even contract to 

 such a degree that their canal is entirely closed, and thus 

 after birth, even without the application of a ligature, 

 as when, for example, the umbilical cord has been torn 

 asunder, the bleeding may stop of itself. The thickness 

 of the walls of these vessels is, therefore, easily compre- 

 hensible, for in addition to the muscular coat, which is 

 of itself so thick, there is an internal, and, though it is 

 certainly not very strongly developed, an external coat ; 

 and only after this do we come to the gelatinous, jelly- 

 like tissue (mucous tissue (Schleimgewebe) ) of the umbili- 

 cal cord. Through these layers, therefore, nutrition 

 would have to take place, if the umbilical vessels were 

 the nutrient vessels of the cord. Now I certainly can- 



FIG. 41. 



Fig, 41. Transverse section through a part of the umbilical cord. On the left is 

 seen the section of an umbilical artery, with a very thick muscular coat, and to this, 

 as one proceeds outwards, succeeds the gradually widening network of cells of the 

 mucous tissue of the cord. 80 diameters. 



