 Four anatomic features must be present for orotracheal intubation to be straightforward : adequate mouth opening ( full range of motion of the temporomandibular joint ) , sufficient pharyngeal space ( determined by examining the back of the mouth ) , sufficient submandibular space ( distance between the thyroid cartilage and the chin , the space into which the tongue must be displaced in order for the larygoscopist to view the glottis ) , and adequate extension of the cervical spine at the atlanto @-@ occipital joint . If any of these variables is in any way compromised , intubation should be expected to be difficult . 
