At the mouth of the oesophagus there is an aganglionic zone similar to that in the anorectal organ of continence. This is part of the system of permanent closure. Since the musculature at the oesophageal entrance is arranged in a screw-like fashion the aganglionic zone lies obliquely to the longitudinal axis of the oesophagus. Closure at the oesophageal entrance is further supported by a kind of corpus cavernosum similar to that in the rectum. In this pharyngeal corpus cavernosum blood is drained between the muscular fibres and their contraction prevents its drainage, thus facilitating the closure of the musculature. The constrictor pharyngeus muscle takes a similar course as does the puborectalis which leads to a bend in the anal canal. Thus also at the entrance to the gastrointestinal tract an arterial angiomuscular system of closure exists in the center of which an aganglionic segment is conspicuous.