420 Mr. Lawson Tait on the 



has no relation whatever to the development of the child), the arteries 

 are to be seen on the outside of the imperfect helix, and this greater 

 length has to be accommodated by twistings and reversions. But even 

 in such a cord sections are to be seen where the spiral becomes complete, 

 and then the arteries take their normal place within the helix. 



Injection of one or both arteries by plaster, with subsequent drying, 

 does not produce a spiral even in cases where the cord has shown a 

 very marked spiral when the vein has been previously distended with 

 water. 



When the spiral is faintly marked but the cord long, and the arteries 

 not very much, if at all, longer than the vein, the spiral will be found 

 always at the end near the foetus. Thus in one specimen, which is very 

 typical of this class, there are three well-marked helices occupying the 

 six inches of the cord at the foetal end. One artery was successfully 

 injected, and it is seen to occupy an almost straight course in the middle 

 of the helices, the uninjected artery accompanying it closely, whilst 

 further on they are both seen to follow, with only one reversion or 

 doubling, the almost straight course of the vein. 



This last fact makes it very evident that the growth of the spiral is 

 directed by some mechanism at the foetal end of the cord, and not by any 

 hypothetical revolutions of the foetus. 



From the appearances of some cords it would also seem as if the spiral 

 growth of the cord became interrupted for a short time, or even reversed, 

 and then that it resumed its original direction. 



In the first and fourth volumes of the ' Encyclopaedia of Anatomy ' 

 some interesting quotations are given by Vrolik and Mr. J. Hart. 

 Yrolik gives some cases where the vessels ran from the foetus to the 

 placenta separately, and not twisted in a cord. He also mentions that 

 extreme shortness of the cord is generally accompanied by ectopia of the 

 abdominal viscera, indicating an arrest of development at an early period 

 of embryogenesis. Bndolphi states that the umbilical vein is persistently 

 double in the Quadrumana of the new world; but I cannot anywhere 

 find a statement as to whether, in such a case, the cord is twisted 

 or not. 



I think we may conclude from some of these facts that both the 

 growth of the cord and its spiral direction are due to some mechanism at 

 the omphalic ring, and that probably that mechanism is in a most im- 

 mediate relation to the umbilical vein. 



Further, I think it certain that the greater part of the spiral, and the 

 closest coils of the spiral, are formed during the later months, or even 

 weeks, of gestation. Thus in cords which are deficient in the spiral it is 

 always most marked near the foetus ; and in one which I have already 

 alluded to as the most perfectly spiral cord I have seen, the helices were 

 complete in an inch and an eighth near the child, whilst they gradually 

 opened out towards the placenta, so that the last was nearly three inches 



