DYSPHAGIA PHARYNGEAL POUCH 227 AETIOLOGY. The upper end of the oesophagus is guarded by a muscle sphincter called the cricopharyngeus which is normally closed. The lower part of the pharynx has a weak area at the lower part of the inferior constrictor muscleŚ the so-called dehiscence of Killian (Fig. 115). At this point there is only a mucosal layer, a submucosa and one layer of muscle fibres. If the patient has the habit of a 'double swallow' and develops an abnormally high intra- pharyngeal pressure during swallowing then this weak area will be subjected Fig. 113. Shows spoon-shaped, brittle nails in the Paterson-Brown Kelly syndrome. Fig. 114. Radiograph to show the Paterson- Brown Kelly syndrome with web. Fig. 115. A ,Site of origin of pouch between oblique and transverse cricopharyngeus; B, Cricopharyngeal sphincter.