Killian's dehiscence is in
Inferior constrictor muscle has two parts. 
Thyropharyngeus with oblique fibres and cricopharyngeus with transverse fibres.
Between these two parts exists a potential gap called "Killian's dehiscence". It is also called "Gateway of tears". 
This is also the site of herniation of pharyngeal mucosa in case of the pharyngeal pouch.
Superior constrictor
Inferior constrictor
Middle constrictor
None