THE UMBILICAL CORD 



433 



serotina, the outlets. At the margin of the placenta the border of 

 this great intervillous lake is relatively free from villi and forms 

 the so-called circular sinus, a space which is obviously not a true 

 sinus, in that, not having a proper wall, it can not be said to pos- 

 sess definite boundaries. 



Since the fetal blood vessels of the placenta are everywhere 

 contained within the connective tissue of the chorionic villi, while 

 the maternal blood circulates only in the intervillous spaces, it is 

 obvious that there can be no direct communication between the 

 fetal and the maternal blood channels, nor can there be any inter- 

 change whatsoever of fetal and maternal blood cells. The course 

 of the fetal blood can be traced from the umbilical arteries to the 

 arteries of the villi, thence through the blood capillaries to the 

 venous radicals within the villi; these return the fetal blood, 

 through veins in the 

 connective tissue of 

 the chorion, to the 

 larger venous branches 

 in the membranous 

 chorion, which finally 

 unite to form the um- 

 bilical vein. 



THE UMBILICAL COED 



This organ trans- 

 mits the two umbilical A 

 arteries which are spi-r! 

 rally wound about the 

 umbilical vein. These 

 vessels are embedded 

 in a non-vascular, gel- 

 atinous, connective 

 tissue, known as the 

 jelly of Wharton, 

 which is rich in cells 

 and ground substance. 

 The fibres, as in all 

 embryonic tissue, are 

 poorly developed and 

 form only a loose net 

 of very delicate fibrils. 

 29 



FIG. 350. TRANSECTION OF THE UMBILICAL CORD 

 OF A NEW-BORN HUMAN INFANT. 



A, artery ; F, F, veins. Hematein and eosin. 

 Photo, x 10. 



