Killian's dehiscence is in
Superior constrictor
Inferior constrictor
Middle constrictor
None
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.