ENLARGEMENT OF THE PREGNANT UTERUS. 445 



most obstetricians, who believe that the os internum dilates, 

 and that the neck is gradually absorbed, as it were, by the 

 body of the uterus, during the later months of pregnancy. 



We have already studied the remarkable changes which 

 take place in the mucous membrane of the uterus during 

 pregnancy and the mode of formation of the decidua, and 

 we have seen that the mucous membrane of the neck does 

 not participate in these changes and is not thrown off in par- 

 turition. The only change, indeed, which we note in the 

 neck, aside from the softening of its texture, is the secretion 

 of the plug of mucus which closes the os. 



The changes in the walls of the uterus during pregnancy 

 are very important. The blood-vessels become much enlarged, 

 and the muscular fibres increase immensely in size, so that 

 their contractions are very powerful when the foetus is ex- 

 pelled. 



It is evident that, on account of the progressive increase 

 in the size of the uterus during pregnancy, it cannot remain 

 in the cavity of the pelvis at the later months. During the 

 first three months, however, when it is not too large for the 

 pelvis, it sinks back into the hollow of the sacrum, the f undus 

 being directed somewhat backward, with the neck presenting 

 downward, forward, and a little to the left. After this time, 

 however, the increased size of the organ causes it to extend 

 into the abdominal cavity, so that its f undus eventually reaches 

 the epigastric region. Its axis then has the general direction 

 of the axis of the superior strait of .the pelvis. 



The enlargement of the uterus and the necessity of car- 

 rying on a greatly-increased circulation in its walls during 

 pregnancy are attended with a temporary hypertrophy of the 

 heart. According to Ho bin, it is mainly the left ventricle 

 which is thickened during utero-gestation, and the increase in 

 the weight of the heart at full term amounts to more than 

 one-fifth. 1 After delivery, the weight of the heart soon re- 

 turns to nearly the normal standard. 



1 LITTRE ET ROBIN, Dictionnaire de medecine, Paris, 1873, Article, Cceur. 



