Final answer:
The posterior lingual sulcus denture extension is limited by the palatoglossus and styloglossus muscles, which are part of the extrinsic muscles of the tongue involved in oral functions such as chewing and swallowing.
Step-by-step explanation:
The posterior lingual sulcus denture extension is limited primarily by the action of two extrinsic muscles of the tongue: the palatoglossus and the styloglossus muscles. The palatoglossus muscle originates on the soft palate and elevates the back of the tongue, while the styloglossus, originating from the styloid bone, allows upward and backward motion of the tongue. The role of these muscles is critical in functions such as positioning food for optimal chewing, forming a bolus for swallowing, and facilitating speech.