* THE PREGNANT UTERUS. 321 



part of them may be followed, on the one hand, until they connect with the blood 

 sinuses of the uterus, and, on the other, until they open into the intervillous 

 spaces, which therefore receive a direct supply of blood from the mother. 



The principal difference to be noted between the uterus before and that 

 after the fifth month in the relations of parts is the presence or absence of the 

 decidua reflexa as a distinct membrane. During the fourth month the reflexa- 

 stretches as the membranes expand, and becomes thinner and thinner until by 

 the end of the fourth month it is as delicate and transparent as the chorion and 

 lies close against the decidua vera. 



Human Uterus Seven Months Pregnant. 



If we examine a pregnant uterus at any time during the sixth to ninth 

 month of gestation, we find essentially the same relations of the parts — the most 

 marked difference being in the size of the uterus, which increases with the dura- 

 tion of gestation, to correspond to the growth of the foetus. A description of a 

 uterus seven months after conception will suffice, therefore, for our present 

 purpose. 



Such a uterus is a large, rounded bag, with muscular walls, and measures 

 seven or eight inches in diameter. Examined externally, it is remarkable espe- 

 cially for the numerous large sinus-like blood-vessels ; its surface is smooth ; the 

 texture of the walls is firm to the touch, but the walls yield to pressure, so that 

 the position of the child can be felt. As the placenta is generally upon the 

 dorsal side, it is usual to open the uterus by a crucial incision upon the ventral 

 side. The walls are about one-half of an inch thick, sometimes more, sometimes 

 less, and as soon as they are cut open we enter at once into the cavity of the 

 uterus containing the foetus and nearly a pint of serous liquid — the amniotic 

 fluid. The foetus normally lies on one side, has the head bent forward, the arms 

 crossed over the chest, the thighs drawn against the abdomen, and the legs 

 crossed; it resembles closely the child at birth, but is smaller; its head is, rela- 

 tively to the size of the body, larger; the abdomen is more protuberant, and the 

 limbs proportionately smaller. The inner surface of the uterus is smooth and 

 glistening; if it is touched with the finger, it is found to be covered by a thin but 

 rather tough membrane, called the amnion, which is only loosely attached. Ex- 

 amination of the uterine wall, where it has been cut through, shows that its 

 thickness is formed principally by the muscular layer, which is made up by 

 numerous laminae of fibers, between which are the large and crowded blood 

 sinuses, similar to those distinguishable on the external surface of the uterus. 

 About one-fifth or less of the wall inside the muscularis has a different texture 

 and can be partly peeled off as two distinct membranes, the innermost of which 



