As the abdomen of the foetus closes up with the advancing development, it is found that the stem of the allantoid vesicle and the umbilical vesicles are embraced in one common sheath, the amnion. And when the abdomen fails to close up firmly and tightly around the cord, there remains what is called a congenital umbilical hernia which continues till the child is perfectly formed. The urinary bladder is formed on the abdominal portion of the urachus or allantoid vesicles. Hence it appears that the bladder is one a line with the cord; and when the child has been separated from the mother and the foetal circulation cut off, the two arteries arising from the bifurcation of the aorta are converted into suspensory ligaments of the bladder which terminate in the umbilicus.
The umbilical cord at full term differs very much in length in different case; it may be but a few inches, or even five or six feet in length; but it is usually from twenty one to twenty-three inches. Neither nerves nor lymphatics have been satisfactorily demonstrated in the cord. Thus are the waters of the amnion severe to protect the foetus as far as possible from external violence, by allowing it easily to float away and evade any direct attack; so the entire absence of direct nervous connection between the foetus and the mother prevents the former from being too injuriously affected by any sudden mental emotion or moral excitement of the latter. The child must indeed be powerfully affected in such causes, but through the circulation only; and thus not so rapidly or so violently as if there were direct nervous communication.
Fig. 57.
An anomaly, described by Benchiser; a division of the cord, just within the membranes, into five or six branches.
The greater part of the body of the umbilical cord is made up of the arteries and vein; but what is very curious, the arteries wind around the cord, from left to right, through its whole length, the vein constituting the central axis of this regular spiral. The cause of this, for it must have a determinate cause, has not been satisfactorily explained; a similar phenomenon may be observed in pouring fluids through a tunnel; they will always gyrate in a simple direction.
It is very common of find the cord found round the child’s neck, at parturition, requiring to be slipped off upon the emergence of the head; in such cases there is probably an abnormal length of the cord. Other cases are reported, in which the cord is tied in knots, but not so tightly as to compromise the foetal life by impeding the circulation. The umbilicus usually constitutes the point of the cord; but it has been known to arise from the head, the chest, the shoulder, &c.; such anomalies result from some peculiarly disordered condition of the mother, during this period of the incipient development of the embryo. It will be observed that as the interior or abdominal portion of the blastodermic membrane represents the organs of the vegetative life, so the umbilical cord, arising form this very portion of the embryo, and connecting with a corresponding portion of the mother,-through the placental mass attached to the uterine walls, directly unites the vegetative organization of the mother with that of the child; this organization, being thus seen to underline the whole organic life, and thus to involve all that we understand by hereditary constitution. The same ideas are also no less plainly suggested by the fact that the whole life of the child is absolutely dependent upon the vital circulation of the mother, the movement of which is entirely under the control of the vegetative, organic, or ganglionic nervous system.
