78. The Cotyledons sometimes consist of only one short and very thick principal trunk—dividing itself, at a short distance from the surface whence it springs, into two, three, sometimes more, lesser trunks, and then again subdividing into thousands of smaller tubes;—at other times the cotyledons consist of two or three distinct straight trunks of different calibre springing from the chorion close to each other (as insulated clusters of lofty and straight trees are often seen here and there on a plain); in which case, the corresponding subdivisions being more numerous, the cotyledon is necessarily larger. (Personal observations, 1825, 1826.) 79. The main trunks of these cotyledons are ramifications of the umbilical vein and arteries, seen to spring from the subdivision of those vessels which are observed to run horizontally on the fœtal surface of the placenta, and which are the termination of the umbilical cord. Between these cotyledons there are spaces of various sizes in which the surface of the Chorion is clear of all filaments, vessels, or any other attachment or projection whatever,—such surfaces are smooth and shining. (Personal experiments, 1825, 1826.)[17] 80. The trunks of the cotyledons and their subdivisions whether springing from the vein or from the arteries of the cord have their coats made of the Chorion and amnion which accompany each cluster so as to form the thinnest pellicular receptacle for their ramifications. It follows hence, that when a coloured liquid, or even air is injected through the arteries of the cord, no escape of the injection takes place, nor can take place, from the terminal vessels of the clusters or cotyledons—and as it is found also that the same injection, if projected long enough (without lacerating any part of the gossamer-like structure we act upon) is brought back by the vein of the cord (which has no valves to prevent such a return) another conclusion is inevitable, namely that the terminal arterial vessels become, by a continuous arrangement, incipient radicles of the venous tubes. (Personal experiments, 1825, 1826.) 81. Now in as much as in the human placenta, expelled at the full period of gestation, before any experiment be undertaken to disturb its integrity, the lobes which it presents have each the appearance of a continuous mass, without any intervening spaces (79); and as these appear only clear, smooth, and shining, after maceration and much patient dissection that leaves nothing rough, or lacerated or divided by violence, behind; it follows that a something must have been removed, during the process of maceration and dissection, which before the employment of those processes occupied the spaces in question. (79.)