THE PREGNANT UTERUS. 345 



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 duration of 

 gestation, to correspond to the growth of the fetus. 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 

 7 or 8 inches in diameter. Examined externally, it is remarkable especially 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 situated normally upon the dorsal side, 

 it is usual to open the uterus by a crucial incision of the ventral wall. 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 

 fetus and nearly a pint of serous liquid the amniotic fluid. The fetus 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 (compare Fig. in). It 

 resembles closely the child at birth, but is smaller; its head is, relatively to the 

 size of the body, larger; the abdomen is more protuberant, and the limbs propor- 

 tionately 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 mem- 

 brane, called the amniqn, which is only loosely attached. Examination of the uter- 

 ine wall, where it has been cut through, shows that its thickness is formed princi- 

 pally 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 distin- 

 guishable 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 is the amnion already mentioned, 

 and the outer is the chorion united with the decidua. The amnion and chorion 

 are appendages of the embryo; the decidua is the modified mucous membrane of 

 the. uterus. Let us return to the embryo. From its abdomen there springs a long, 

 whitish cord, known as the umbilical cord; it is usually .from about one third to 

 one half an inch in diameter and 40 cm. long, but its dimensions are extremely 

 variable; it always shows a spiral twist, and contains three large blood-vessels, two 

 arteries and one vein, all of which can be distinguished through the translucent 

 tissue. The distal end of the cord is attached to the wall (placenta) of the uterus 

 usually near the middle of the dorsal side of the organ. It is easily seen that the 

 blood-vessels of the umbilical cord radiate out from its end over the surface of the 

 uterus underneath the amnion, branching as they go; they spread, however, only 

 over a circumscribed area, the placental, where the wall of the uterus is very 

 much thickened. A vertical section through the placental area -shows that the am- 

 nion and chorion are widely separated from T;he decidua and muscularis by a 



