[Sequential innervation of the intestinal loop in the human embryo].

The study of 20 excellent human embryos of the Carnegie Collection has allowed the innervation of the intestinal loop to be traced during the embryonic period proper. It follows the centrifugal sequence observed throughout in the development of the peripheral nervous system. At stage 14 or 15, the rami comunicantes and the primordium of the latero-vertebral sympathetic trunk appear. Splanchnic fibres are noted at stage 16, and at stage 17 the superior mesenteric plexus appears. Then nerve bundles progress along the superior mesenteric artery according to the following sequence: 1) Nerves fibres face the mesentery (stage 19), 2) They penetrate into the mesentery (stage 20), 3) Nerve buds move forwards and nerve fibres begin to be anchored to the muscular layer of the proximal portion of the loop, duodenum and colon (stage 21), 4) Nerve fibres are anchored to the muscular layer of the middle part of the intestinal loop (stage 22), 5) The nerve buds reach the distal part of the loop in the umbilical cord.