The uterine portion of the placenta covers its convex surface in the form of a thin membrane, and detaches innumera ble fine processes into the substance of the part. It seems to be a portion of the decidua. It is connected into one mass with the umbilical portion, and the ves sels of the uterus are continued into it, although they have no discoverable coin. munication with the umbilical arteries and veins.
The membranes are three in number ; amnion, chorion. and decidua.
The amnion is firm, thin, transparent, and possessing no visible vessels. It im mediately includes the liquor amnii and child The chorion lies outside of the amnion, and adheres to it ; it is transpa rent, very thin and tender, and adheres externally to the decidua.
The decidua is an efflorescence of the internal coat of the uterus, produced af ter conception, in order to adapt the womb for the ovum which is to enter it. It is shed after every birth, or miscar riage, with the other membranes ; and lien, e its name. It is thicker, but more delicate and tender, than the amnion or chorion. It contains several blood ves sels, which are best seen in recently dis charged secundines. It adheres closely to the uterus on one side, and to the chorion on the other. The laceration of the vessels, which this membrane re ceives from the,uterits, accounts for the hemorrhage which follows its separation. At the edge of the placenta it divides into two layers, which pass over the two sur faces of that organ, and form its uterine portion.
The liquor amnii is the fluid immedi ately surrounding the body of the child, and so called from the membrane enclos ing it. Its usual quantity is about two pints. It is a clear, transparent fluid.
The child, while in the uterus, is natu rally contracted into an oval form, adapt ed to the figure and circumstances of its habitation. The vertex of the head makes one end of the oval, and the nates the other. One side or edge of the oval is formed by the occiput, the back part of the neck, and the incurvated trunk ; the other is made by the forehead and the mass of contracted and conglomerated limbs. The chin is close to the breast, the trunk bended forwards, the knees close to the fore parts of the hypochon dria, the legs drawn to the back parts of the thighs, and the upper extremities contracted into the vacant space betwixt.
the forehead and knees. The more or less compact form of the child depends on the quantity of the liquor amnii ; when that is small, the uterus moulds the child into various forms, and often produces defor mities of the limbs. The head is placed downwards with respect to the mother, and the nates upwards.
The usual weight of the child at the time of birth is from five to eight pounds ; of several thousands weighed at the Bri tish Lying-in Hospital, the largest weigh ed 11/b. 2oa. the smallest was above 41b.
The head, upper part of the trunk, and per extremities, are very large, when mpared with the lower parts of the dy. The surface of the skin is covered etty generally with a white sebaceous atter.
reculiarities in the Structure of the Fens.
These are on the whole numerous ; but we shall briefly enumerate the most im portant only.
The first which claim our attention are, some points respectii.r the heart and large-blood-vessels ; which we may sup pose absolutely necessary to the life of the child, while it draws nourishment from the mother, and cannot enjoy respi ration. As the foetus in utero cannot breathe, the circulation of its blood through the lungs would be useless : hence that fluid can go from the right to the left side of the heart by means of an opening called the foramen ovale, and placed between the two auricles, and of a communicating canal from the pulmo nary artery to the aorta, called ductus ar teridsus. The umbilical arteries are con tinuations of the internal i I iacs, taking the blood from the child to the placenta ; from which it is brought back by the um bilical vein, and circulated through the liver.
The lungs are small and compact ; and as they have not yet received air, they are specifically heavier than water. This is an important point, and is usually re ferred to in trials for child-murder, in or der to determine whether the child was born alive or no. If the lungs sink in wa ter, it is considered a still-born case ; and if they float, the probable inference is, that the child has breathed, but it would be a very rash conclusion that it had, therefore, been murdered. Much cau tion and consideration ofconcomitant cir cumstances must be employed in making use of this proof. Putrefaction will dis engage air that may make the lungs float.