EXERCISE THE FIFTY-THIRD.
Of the inferences deducible from the course of the umbilical vessels in the egg.
We find the blood formed in the egg and embryo before any other part ; and almost at the same moment appear its receptacles, the veins and the vesicula pulsans. Wherefore, if we regard the punctum saliens as the heart, and this along with the blood and the veins as constituting one and the same organ, conspicuous in the very commencement of the embryo, although we should admit that the proper substance of the heart was deposited subsequently, still we should be ready to admit with Aristotle that the heart (an organ made up of ventricles, auricles, vessels, and blood) was in truth the principal and pri- mogenate part of the body, its own prime and essential element having been the blood, both in the order of nature and of ge- netic production.
The parts that in generation succeed the blood are the veins, for the blood is necessarily inclosed and contained in vessels ; so that, as Aristotle observes, we find two meatus venales even from the very first, which canals, as we have shown in our his- tory, afterwards constitute the umbilical vessels. It seems ne- cessary, therefore, to say something here of the situation and course of these vessels.
In the first place, then, it is to be observed that all the ar- teries and veins have their origin from the heart, and are as it were appendices or parts added to the central organ. If there- fore you carefully examine the embryo of the human subject, or one of the lower animals, and having divided the vena cava between the right auricle and the diaphragm, look into it up- wards or towards the heart, you will perceive three foramina, the largest and most posterior of which tending to the spine is the vena cava; the anterior and lesser proceeds to the root and trunk of the umbilical vessels ; the third and least of all enters the liver and is the origin and trunk of all the ramifications distributed to the convexity of that organ. Whence it clearly
