Innervation of duodenum and ductus choledochus in human embryo.

Abstract

In the duodenum of fourth month human embryo, the intramural nerve cells show an infantile stage of development represented by spherical cells with a large round nucleus. In the cell bodies neurofibrils are as yet scarcely formed. Mantle cell nuclei are much smaller than the nerve cell nuclei in size and at this stage of embryonic life, are much smaller in number than those in human adults. The mitosis of these cell nuclei is considered to take place gradually in later days. In seventh month embryo, the nerve cells increase somewhat in size, but the majority is. still represented by spherical cells with a large round nucleus, except a minority of the cells, by which neurofibrils and a few nerve processes begin to appear, showing the formation of incipient simple multipolar cells. Mantle cell nuclei are more numerous than in fourth month embryo but far lesser than in human adult. The vegetative terminalreticulum is in a nearly perfect formation already in the fourth month on the embryonic life, as has been established by many researches in this laboratory, and also in my specimen of embryonic duodenum, this doctrine has been beautifully confirmed. In the seventh month embryo, the terminalreticulum is even better developed and surrounding the sundry tissue cells enter into tactile control over them. The Schwann's nuclei found in the terminalreticulum I take to be endocrinal in character, as declared by my predecessors. It is of interest that the opening part of the ductus choledochus of fourth and seventh month embryos is as richly provided with vegetative fibres as are the stomach and the intestines. The formation of well-developed vegetative plexus is seen in the connective tissue layer in the periphery of the choledochus, and in places, vegetative nerve cell groups, though somewhat smaller than those in Auerbach's and Meissner's plexus, are observable. The development of the nerve cells and the mantle cell nuclei is on a similar stage as in the duodenum. Numerous nerve branches are sent out from the plexus, which ramify into more minute branches and anastomose at frequent intervals. The minutest of them finally go over into vegetative terminalreticulum, which spread out widely in all the layers of the choledochus and stand in tactile control over the sundry tissue cells. I have succeeded in proving the existence of medullated sensory fibres and their terminations not only in the duodenum but also in the choledochus of fourth and seventh month embryos. The pains caused by pathological disturbances in the duodenum and choledochus could be thus attributed to the existence of sensory terminations in these parts. Large nerve bundles containing numerous sensory fibres which are presumably originated from the splanchnic nerves reach the contact area of the head of the pancreas and the duodenum and thence the major part runs to the duodenum and the rest to the pancreas and the choledochus. The numerous sensory fibres that reach the adventitia of the duodenum run through the outer muscle layer into the Auerbach's plexus and thence into the submucosa through the inner muscle layer to terminate in the submucosa or further in the mucous membrane. In these layers, the sensory fibres lose their myelin and branch out into rami, which, upon running winding courses with peculiar change in size, spread out widely and terminate sharply. The terminal branches sometimes reach the surroundings of the duodenal glands or the epithelium of the crypts and villi, but never penetrate into the cells of the glands and epithelium themselves. The above described sensory fibres are of course much better developed in seventh month embryo than in fourth month one. Many sensory nerve fibres are also seen penetrating into the plexus found in the periphery of the embryonic choledochus. These fibres run also here into the mucous membrane and end in unbranched and simple branched terminations therein. Their terminal fibres end sharply.