Final answer:
The parotid duct opens into the oral cavity near the second upper molar tooth, and it is one of the major salivary glands that secrete saliva into the mouth.
Step-by-step explanation:
The parotid duct, associated with the parotid glands which are located between the skin and the masseter muscle near the ears, opens into the oral cavity in the vicinity of the second upper molar tooth. These glands are one of the three pairs of major salivary glands and are essential for secreting saliva, which enters the mouth through this duct. The oral cavity is a complex structure that includes the inner gums and teeth, the cheeks and lips, and extends towards the oropharynx and fauces. The parotid duct's opening is an important anatomical feature that facilitates the introduction of saliva into the mouth, assisting in the initial digestion of food and maintaining oral health.