THE UMBILICAL CORD. 127 



farther up this vascular part extends, the greater the 

 development of the navel. When the vascular layer is 

 prolonged but a very short distance the navel is greatly 

 depressed ; when it reaches a long way up, a prominent 

 navel is the result. The capillaries mark the limits of 

 the permanent tissue ; the deciduous portion of the cord 

 has no vessels of its own. 



This condition, which seems to be of great importance 

 as regards the theory of nutrition, can be very easily 

 seen with the naked eye in injected foetuses of five 

 months and upwards, and in new-born children. The 

 vascular layer terminates by a nearly straight line. 



Preparations of this sort do not, to be sure, furnish 

 absolute proof, for there might happen to be a few 

 minute vessels proceeding farther up, but invisible to 

 the naked eye. But I formerly made this very point 

 the subject of special investigation, and although I in- 

 jected a number of umbilical cords, some from the arte- 

 ries, and others from the veins, I never succeeded in 

 discovering a single collateral vessel, however minute,, 

 that passed the limits of the persistent layer. The whole 

 of the deciduous portion of the umbilical cord, that long 

 portion which lies between its cutaneous end and its ter- 

 mination in the placenta, is entirely destitute of capilla- 

 ries, and there really exist no other vessels in it than 

 the three large trunks. Now these are all of them re- 

 markable for the great thickness of their walls, which, 

 as we have really only known since the investigations of 

 Kolliker, are enormously rich in muscular fibres. 



In a transverse section of the umbilical cord it may be 

 observed, that the thick middle coat of the vessels is 

 entirely composed of smooth muscular fibres, lying in 

 immediate contact one with the other, and in such abun- 

 dance as is scarcely to be seen in any completely 

 developed vessel. This peculiarity explains the extra- 



