764 



DISCHARGE OF FCETUS AND PLACENTA. 



name of the umbilical cord. It contains the bloodvessels passing out 

 from the body of the embryo to the chorion and placenta. 



After the third month the umbilical cord and its bloodvessels elongate 

 even more rapidly than is required by the increase in size of the amniotic 

 cavity. They consequently assume a twisted form, the two umbilical 

 arteries winding round the vein in a spiral direction. 



The direction of the spiral is not always the same. Prof. McLane 

 has recorded observations made in regard to this point upon 260 um- 

 bilical cords at term, partty in his private practice and partly at the 

 Nursery and Child's Hospital, New York. Of this number, in 138 

 cases the direction of the spiral was from left to right ; in 112 cases, 

 from right to left; and in the 10 remaining instances it was doubtful, 

 the twist being too imperfectly marked for decision. This gives nearly 

 the following percentage as the result of all the observations : 



DIRECTION OF THE SPIRAL TWIST OF THE HUMAN UMBILICAL CORD. 



From left to right 53 per cent. 



From right to left 43 " 



Indeterminate 4 " 



Fig. 276. 



100 



There is, accordingly, no 

 marked preponderance in fre- 

 quency of the twist in either 

 direction. Two cases of twins 

 are included in the above list ; 

 in the first of which both um- 

 bilical cords turned from right 

 to left ; in the second, one of 

 them turned from right to left, 

 the other from left to right. 

 In two instances, the cord 

 presented turns in opposite 

 directions in different parts of 

 its length. 



The gelatinous matter, al- 

 ready described as existing 

 between the amnion and cho- 

 rion, and which disappears 

 elsewhere, accumulates, on 

 the contrary, in the cord in 

 considerable quantity, cover- 

 ing the vessels with a thick, 

 elastic envelope, which protects them from accidental compression or 

 obliteration. The whole is covered by an extension of the amnion, 

 which is continuous at one extremity with the integument of the abdo- 

 men, and invests the cord with an uninterrupted sheath, like the finger 

 of a glove. 



PREGNANT HUMAN UTERUS AND ITS 

 CONTENTS, about the end of the seventh month ; 

 showing the relations of the cord, placenta, and 

 membranes. 1. Decidua vera. 2. Decidua reflexa. 

 3. Chorion. 4. Amnion. 



