ENLARGEMENT OF THE AMNION. 



631 



Fig. 230. 



HCMAN OVCM at end of third mouth, bhowing 

 enlargement of amaiou. 



ning of the fifth month, comes in contact with the internal surface 



of the chorion. Finally, toward the end of gestation, the contact 



becomes so close between these 



two membranes that they are 



partially adherent to each 



other, and it requires a little 



care to separate them without 



laceration. 



The quantity of the amniotic 

 Quid continues to increase dur- 

 ing the latter period of gesta- 

 tion in order to accommodate 

 the movements of the foetus. 

 These movements begin to be 

 perceptible about the fifth 

 month, at which time the 

 muscular system has already 



attained a considerable degree of development, but become after- 

 ward more frequent and more strongly pronounced. The space 

 and freedom requisite for these movements are provided for by the 

 fluid accumulated in the cavity of the amnion. 



The umbilical cord elongates, at the same time, in proportion to 

 the increasing size of the amniotic cavity. During its growth, it 

 becomes spirally twisted from right to left, the two umbilical arte- 

 ries winding round the vein in the same direction. The gelatinous 

 matter, as already described as existing between the amnion and 

 chorion, while it disappears elsewhere, accumulates in the cord in 

 considerable quantity, covering the vessels with a thick, elastic en- 

 velope, which protects them from injury and prevents their being 

 accidentally compressed or obliterated. The whole is covered by a 

 portion of the amnion,. which is connected at one extremity with the 

 integument of the abdomen, and invests the whole of the cord with 

 a continuous sheath, like the finger of a glove. (Fig. 231.) 



The cord also contains, for a certain period, the pedicle or stem 

 of the umbilical vesicle. The situation of this vesicle, it will be 

 recollected, is always between the chorion and the amnion. Its 

 pedicle gradually elongates with the growth of the umbilical cord ; 

 and the vesicle itself, which generally disappears soon after the 

 third month, sometimes remains as late as the fifth, sixth, or seventh. 

 According to Prof. Mayer, of Bonn, it may even be found, by care- 

 ful search, at the termination of pregnancy. When discovered in 



