418 Mr. Lawson Tait on the 



opinion that at the time o£ the commencement of the torsion the right 

 iliac artery appears more like the continuance of the aorta than the left, 

 the latter appearing more like a branch, the right having, therefore, a 

 stronger blood-stream than the left; it would thus influence the foetus. 

 This supposition is ingenious ; but I cannot find any fact which will 

 support it. I have examined several foetuses from the ninth to the 

 sixteenth week without being able to discover any difference in the right 

 and left iliac arteries. Such difference, if it exist, should continue during 

 the growth of the cord ; and I have entirely failed to find any evidence of 

 it in any of the large number of foetuses I have examined. Moreover, 

 it seems greatly contradicted by the fact established by Hecker, that the 

 twist is once to the left for 3*5 times to the right. Further, are we to 

 suppose that in the cases of well-matured children in whose cords there 

 are no twists, or only very slight ones, the embryo has continued perfectly 

 still in the cavity of the amnion ? 



Neugebauer (' Morphologie der menschlichen JNTabelschnur,' Breslau, 

 1858) explains the rotation by the pressure of the blood-stream on the 

 walls of the vessels. The umbilical vein, he states, has a greater area 

 than the two arteries together, and is more distended, the pressure 

 diminishing its growth in length, whilst that of the arteries is unin- 

 terfered with, and the natural arrangement must be spiral. Whatever 

 be the explanation, it is a fact which my injections and dissections have 

 established beyond dispute, that the arteries have a greater length than 

 the vein in very many cases, but it is not true in all. 



In some cords the vein is longer than the arteries, for it remains spiral 

 whilst they go almost straight. In others the vein continues persistently 

 and regularly a definite spiral direction, whilst both arteries course over 

 it first in one direction and then excentrically in another, sometimes even 

 turning back over their first course and presenting a varicose appearance 

 on the cord, to return again to their normal direction. Neugebauer 

 states what is in strict accordance with my own experience, that irregular 

 twistings are very common on the arteries but very rare on the vein. I 

 have never seen one on the vein. 



JNeugebauer further believes that the reason the majority of cords are 

 twisted from right to left lies exclusively in a dissimilarity in the size of 

 the arteries. He has found (in agreement with Simpson) that the right 

 artery is larger than the left. Occasionally, he states, the left is the 

 larger of the two, and then the twist is reversed. 



Hyrtl (' Lehrbuch der Anatomie des Menschen ') states that the left 

 artery is usually the larger of the two. I do not see, in the writings of 

 either of these two authorities, any details of the method of examination 

 of their specimens. 



My own method has been to remove the whole thickness of the 

 abdominal wall from the base of the bladder up to and including the 

 omphalic ring, along with a piece of cord. This I place in my freezing- 



