Embryogenesis Reveals the Role of the 'Second Brain' in Digestion (image) CNRS Share Print E-Mail Caption The enteric nervous system in a 16-day old chicken embryo, the point at which it begins to control muscular contractions in the gut. This neural network is located in between circular and longitudinal muscle layers and controls them. Credit Nicolas Chevalier et al. Usage Restrictions None Share Print E-Mail Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.