Page:Laboratory Manual of the Anatomy of the Rat (Hunt 1924).djvu/109

Rh the anterior end of the uterine horn to the dorsal body wall near its union with the diaphragm.

The ovary of most mammals is not inclosed in a capsule. The ova which break through the wall of the ovary pass directly to the opening (ostium abdominale) of the uterine tube, and are then carried by cilia in the tube to the uterus. The following events, however, are said to accompany ovulation in the rat. The periovarial cavity is filled with fluid at the time of ovulation. The bursa ovarica exerts pressure upon this fluid as the result of the contraction of the muscles located near the infundibulum tubae and the attachments of the uterine tube. Simultaneously muscular contractions expand the opening (ostium) of the infundibulum tubae. Thus the fluid within the bursa ovarica, with the contained eggs, is forced into the uterine tube, where muscular contractions, possibly assisted to some extent by ciliary action, carry them to the uterus.

The fertilized egg is implanted in the wall of the uterus, where it develops. Examine a female rat with well advanced fetuses in the uterus. Note the large size of the uterus, its abundant blood supply, and segmental character. Each segment contains a fetus. Slit a segment lengthwise along its ventral surface and expose the fetus. This is covered with a thin membrane, the amnion. Carefully open the amnion along the back of the fetus. The fluid in the amniotic cavity protects the embryo from sudden jars. Note the discoidal placenta on the dorsal side of the uterus. The umbilical cord connects the belly of the embryo with the center of the placenta. The blood of the fetus passes through the umbilical cord to and from the placenta, where by osmosis, it receives nutriment from the maternal blood and surrenders waste materials to the mother's blood. The blood of fetus and mother do not mix in the placenta, but are everywhere separated from each