Killian's dehisence is seen in ?

Ans. is 'c' i.e., Cricopharynx Inferior constrictor muscle has two pas :- (i) Thyropharyngeous with oblique fibres, and (ii) Cricopharyngeous with transverse fibres. Between these two pas of inferior constrictor exists a potential gap called Killan's dehiscence. It is also called the gateway to tear as perforation can occur at this site during esophagoscopy. It is also the site for herniation of pharyngeal mucosa in case of pharyngeal pouch.