Anatomy of the Umbilical Cord. 421 



in length. This could not be the case i£ the twisting were due to the 

 rotation of the foetus during early embryonic life, as then we should 

 expect that the spiral would be uniformly spread over the cord, if, indeed, 

 it would not be most marked near the placenta. Neugebauer says that 

 the spirals have a uniform length, with the exception of those close to 

 the placenta, which are almost invariably longer. 



In his ' Cellular Pathology,' Professor Yirchow gives a drawing 

 of the umbilical cord, and the following description of its vessels : — 

 " The only capillary vessels which are found in the whole length of 

 the umbilical cord of a somewhat developed foetus do not extend 

 more than about 4 or 5 lines (in rare instances a little further) 

 beyond the abdominal walls into that part of the cord which remains 

 after birth. The further 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 depressed. The capillaries mark the 

 limits of the permanent tissue ; the deciduous portion of the cord has 

 no vessels of its own." 



I have made many very careful injections of foetuses of various ages 

 in order to verify this observation. For a long time I was quite unable 

 to do so, and I had the impression that Virchow had mistaken a part of 

 the dermal ring, with the epithelium rubbed off, for a part of the true sub- 

 stance of the cord. Prom a large number of observations I have found that 

 the dermal ring runs on to the cord in a camb-like shape (Plate 11. fig. 1) — ■ 

 that is, that the length of the ring is unequal all round, the greatest 

 length corresponding generally to the position of the vein at the upper 

 part of the ring (Plate 11. fig. 2). This, however, is not constant. At 

 this point the capillary plexus is shown in Yirchow's drawing ; and from 

 a completion of Yirchow's partial observation, it seems to me that in this 

 arrangement we have the immediate mechanism of the spiral growth of 

 the cord. 



The necessities which have evolved it are probably those of the erect 

 position of the human animal, by which the foetus, resting on the brim 

 of the pelvis, might compress the cord to an unsafe extent. This com- 

 pression would be better resisted by a spiral cord than by a straight one, 

 Further, the form of the human uterus, and the occurrence of single 

 gestation as a rule, favour movements of the foetus in all directions ; so 

 that it is well known to the tocologist that the foetus frequently changes 

 its position, though nothing like revolutions are known. During these 

 movements, however, the child might make one or more revolutions, 

 and these might have a disastrous result if the cord were straight ; 

 but it being already twisted, a few revolutions in the direction of the 

 twist could do no harm in the way of occluding the vessels, nor could a 

 few revolutions in the direction of untwisting it be at all likely to be 

 hurtful. 



John Goodsir has shown how thoroughly the spiral runs through all 



