Innervation of Vasa Umbilicalia and Proximal Adherent Part of Umbilical Cord

Abstract

If the silver impregnation is effective enough, it will be clearly seen that in the umbilical cord neither the blood vessels nor the embryonic connective tissue is provided with nerve fibres.
Even vasa umbilicalia in the ventral abdominal wall before entering the umbilical cord, are devoid of tunica externa, unlike the common blood vessels, so that no existence of perivascular nerve plexus is possible. Consequently, it must be assumed that the placental circulation through the umbilical cord is passively governed by the nerve center supplying the root parts of the vasa umbilicalia. This absence of any nerve accompanying these blood vessels may be a fortunate arrangement not only for their connective tissue closure in the abdominal wall but also for the decease and deciduation of the umbilical cord after birth.
The transitional part from the ventral abdominal wall to the umbilical cord is a mixture of both of them in histological structure, showing some resemblance with the former but more with the latter. It is covered by a thin squamous epidermis with a fibrous connective tissue layer formed subepithelially, though in a lower development than in the abdominal wall, and the space surrounding the vasa umbilicalia running through the center of this part is filled with embryonic connective tissue. Sweat glands are present, though in a weak development, and hair roots are as a rule lacking. Minute blood vessels, capillaries and lymph vessels are also found running into the part. This transitional part is about 5mm in length in tenth month embryos, is marked off by astringent grooves from the umbilical cord as well as the ventral abdominal wall, and is destined to become the navel after birth.
The transitional part is supplied with nerve fibres, but not along the vasa umbilicalia nor in the embryonic connective tissue surrounding them. The nerve fibres run along the small blood vessels and are mostly of vegetative nature. Their temination spreads out as the typical terminalreticulum subepithelially already in fourth month embryos. On the contrary, sensory fibres are very small in number, and their terminations are probably represented by unbranched terminations, but I could not make out them with adequate clearness.
More nerve fibres are found in the skin of the abdominal wall around the transitional part than in the transitional part. They consist of sensory and vegetative fibres, the latter of which come into frequent anastomosis with the perivascular plexus, first form nerve plexus in the sudoriferous layer, then run through the reticular layer into the papillary layer. The sensory fibres, however, mostly run toward the SETO's hair-nerve shields and tubes as sensory hair-nerve fibres, to end therein. Their terminatione are represented in tenth month embryos as comparatively simple plexus-like and non-descript terminations and are inferior in development to those in the common ventral abdominal wall in the same month embryos described by AZUMA (1951). The numbers of the hair-nerve shields and tubes as the terminal territories are nearly equal in this part, so it may be assumed that the skin here is rather sensitive.
The papillary layer of the corium is well provided with vegetatire nerve fibres, but with only a very small number of sensory fibres mostly derived from sensory hair-nerve fibres. The sensory terminations are here merely represented by unbranched terminations ending sharply or sometimes bluntly, even in tenth month embryos.