THE UMBILICAL VESSELS. 205 



ligaments. They are exterior to the peritoneum, and contained 

 in a duplicature of it. 



A vein also called the Umbilical, which is much larger in 

 diameter than both of the arteries, returns from the placenta 

 along the cord, and enters the cavity of the abdomen at the 

 umbilicus. It proceeds thence, exterior to the peritoneum, 

 but in a duplicature of it called the Falciform Ligament, to 

 the liver, and enters that viscus at the great fissure ; along 

 which it passes to the left branch of the sinus of the vena 

 portarum, into which it opens and discharges the blood which 

 flows through it from the placenta. It opens on the anterior 

 side of the branch of the vena portarum, and from the posterior 

 side of the branch, opposite to this opening, proceeds a duct or 

 canal, which opens into the left hepatic vein near its junction 

 with the vena cava. This communicating vessel is called the 

 Ductus, or Canalis Venosus ; to distinguish it from the duct 

 which passes from the pulmonary artery to the aorta, and is 

 called Ductus, or Canalis Arteriosus. This venous duct car- 

 ries some of the blood of the umbilical vein directly to the vena 

 cava ; but it is much smaller than the umbilical vein, and of 

 course a considerable quantity of the blood which passes 

 through the umbilical vein must pass through the liver by the 

 vena portarum, before it can enter the cava. 



In some foetal subjects, if a probe of sufficient length be in- 

 troduced within the umbilical vein, and pushed forwards, it will 

 pass to the heart, without much difficulty or opposition, 

 as if it proceeded along one continued tube, although it really 

 passes from the umbilical vein across the branch of the vena 

 portarum, and then through the ductus venosus, and through 

 a portion of the left hepatic vein, into the inferior vena cava. 



If the umbilical vein be injected with a composition, which 

 will be firm when cool, it appears to terminate in a rounded 

 end, which is situated in the transverse fissure of the liver : the 

 sinus of the vena portarum, into which this vein enters, appears 

 like two branches going off, one from each side of it, and the 

 ductus venosus like a branch continuing in the direction of the 

 main trunk of the umbilical vein. 

 VOL. II. 18 



