UMBILICAL CORD. 371 



the mode of development of the chorion and the amnion, it 

 is evident that the umhilical cord is nothing more than the 

 pedicle which connects the embryon with that portion of the 

 chorion which enters into the structure of the placenta. It 

 is, indeed, a process of the allantois, in which the vessels 

 eventually become the most important structures. The cord 

 is distinct at about the end of the first month ; and, as devel- 

 opment advances, the vessels consist of two arteries coming 

 from the body of the foetus, which are usually twisted from 

 left to right around the single umbilical vein. In addition 

 to the spiral turns of the arteries around the veins, the entire 

 cord may be more or less twisted, probably from the move- 

 ments of the foetus. 



The fully-developed cord extends from the umbilicus of 

 the foetus to the central portion of the placenta, in which its 

 insertion is usually oblique; though it may be inserted at 

 other points, and even outside of the border of the placenta, 

 its vessels penetrating this organ from the side. Its usual 

 length, which varies very considerably, is about twenty inches. 

 It has been observed as long as sixty, and as short as seven 

 inches. 1 When the cord is very long, it sometimes presents 

 knots, or may be wound around the neck, the body, or any 

 of the members of the foetus ; and this can only be accounted 

 for by the movements of the foetus in utero. 



The external covering of the cord is a process of the 

 amnion, which, as it extends over the vessels, includes a 

 gelatinous substance, the gelatine of "Wharton, which sur- 

 rounds the vessels, and protects them from compression. 

 This gelatinous substance is identical with the so-called mem- 

 brana intermedia, or the substance included between the am- 

 nion and the chorion. The entire cord, covered with the 

 gelatine of "Wharton and the amnion, is usually about the 

 size of the little finger. According to Robin, the normal 

 cord will sustain a weight of from ten pounds and ten ounces 



1 YROLIK, Cyclopaedia of Anatomy and Physiology, London, 1849-1852, vol. 

 iv., part ii., p. 947, Article, Teratology. 



