3007. The osseous and muscular system first makes its appearance, when the vegetative parts are present.
3008. The intestines, the vessels, and the commencement of the sexual parts are originally situated in the umbilical cord, which is itself surrounded by the integument. The umbilical cord is therefore nothing else than the posterior extremity of the body or abdomen, through which the embryo respires and is nourished.
3009. The first respiration and deglutition is therefore a respiration and deglutition effected by the sexual parts, as in the lowest animals.
b. Functions of the Fœtus.
1. Nutrition.
3010. The juices which are contained in the developmental sacs are nutritive juices or chyle; they contain principally albumen. The chyle of the intestinal vesicle depends upon the vitellus.
3011. The fœtal water in the amnion is derived from albumen in the ovum; it is here secreted by the oviduct, but in the Mammalia by the internal wall of the uterus, and absorbed by the general envelopes.
3012. The cause of this secretion resides in the decomposition of the blood through the influence of the chorion. Thus if the maternal blood become deoxydized, it must necessarily revert to the condition of chyle. This chyle is the fœtal water.
3013. The fœtal water is absorbed by the embryo through the integument.
3014. No blood is transferred from the mother directly to the fœtus.