74. The umbilical vein and the arteries are spirally twisted together and in the majority of cases they are so from left to right. (Hunter.) The former contrivance is evidently intended for the purpose of giving the greatest possible extension of tubular passage for the blood compatible with the smallest increase in the length of the cord. The cord which is very short at five or six weeks, becomes at the conclusion of gestation from one foot six to two feet long. (Chaussier.)
75. The umbilical arteries, two in number, are a continuation of the primitive iliac arteries; they pass over the lateral regions of the bladder, ascend along the internal surface of the anterior abdominal covering of the fœtus, approaching each other as they get nearer to the navel, through which they emerge in order to enter the sheath of the cord, winding round the vein in their way to the placenta. (77) The vein on the contrary which proceeds from the placenta is of a larger calibre than that of the two arteries taken together. It is soft and extensible—and after having slightly meandered within the umbilical sheath penetrates through the navel into the abdomen of the fœtus, directs its course towards the inferior surface of the liver, enters the antero-posterior fissure of that viscus, unites with the left branch of the hepatic and vena portarum, and reaches under the name of the venous duct, the inferior cava. It has no valves, except one at its intro-abdominal bifurcation. This vessel, throughout its course, becomes obliterated after birth.
76. The omphalo-mesenteric vessels consist of a vein and an artery, the ramifications of which, externally to the fœtus, are seen distinctly on the umbilical vesicle (vesicula intestinalis). They accompany the cord as far as the navel through which they pass into the abdomen. They then separate, the former proceeding on the right to join the trunk or one of the branches of the mesenteric vein, and the latter on the left to join the superior mesenteric artery. These vessels are obliterated, as the vesicula umbilicalis to which they belong disappear, and lastly disappear in their turn. They have, however, been observed sometimes in the cord of the full grown fœtus, like whitish solid filaments. (Chaussier, Beclard.) In the recent case of an individual twenty years of age, who died of consumption, these vessels were found as pervious as when existing in the embryonic state, and contained blood. (Spakenberg.)[[16]]
77. When the Ovum is advanced to the second or third month of its fecundated existence (for the period varies in different examples I have had under my observation); its attachment to the Uterus, is firm and complete. Many of the vessels of the external surface of the chorion, which by this time have increased in size, while their free ends have luxuriantly branched out in innumerable minute vessels, have clustered together and formed what are in reality cotyledons—by means of which the said attachment is principally effected. (Personal observations and experiments.) The congeries of these clusters of vessels constitute the principal part of what has been called the Placenta, which grows in size and expands as the gravid uterus expands progressively during gestation.
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.)
82. That something consists in a congeries of blood-vessels, arterial as well as venous, proceeding from the longitudinal vessels of the decidua covering the placenta (Dr. Hunter, Chaussier, Meckel, Lesauvages, myself). These vessels ramify in a manner analogous to that in which those of the fœtus have been described to ramify, (78, 79.) They penetrate between the interstices left by the minutest branches of the umbilical cotyledons. Their direction is lateral, perpendicular, oblique, and variously tortuous, in reference to the plane of the decidua whence they originate. Wherever they form a thick cluster, they are found to occupy one of the spaces already described (79). To facilitate this arrangement, and to render the distribution of the decidual vessels throughout the masses of the umbilical cotyledons more effectual—the membrane itself (decidua) is found to dip among the latter, dividing the general mass into lobes of various sizes, by which contrivance the decidua acquires an additional extension. (Personal Observations and Experiments.)
83. The decidual vessels are formed by continuous arterio-venous tubes. They reach, but do not connect themselves with the chorion. In the same manner as the terminal vessels of the umbilical cotyledons reach, but do not connect themselves with the superimposed decidua. When an attempt is made to remove (peel off) the latter from the surface of the placental mass, we notice certain attachments between them which are torn in the removal. These are the decidual vessels (82) and not as stated incorrectly by some, the terminal vessels of the umbilical system. (Recent German, and French, and Personal Experiments.) In the same manner as the umbilical vessels are accompanied by the chorion, the decidual vessels are accompanied by a membrane peculiar to the placenta, which I have called the membrana propria.