The main part of the parotid gland lies in a recess bounded in front by the ramus of the jaw, with the masseter externally and the internal pterygoid internally ; the mastoid process and the sterno-mastoid muscle behind ; the temporo-maxillary joint and external auditory meatus above ; and a horizontal line from the angle of the jaw to the sterno-mastoid below. By extending the head and pushing forward the lower jaw the space is increased in size, while by opening the mouth widely the upper portion of the space is increased by gliding forward of the condyle, and the lower portion is diminished. The gland is enclosed in a process of the cervical fascia, which splits to enclose it, and which sends in numerous septa, subdividing the gland. The superficial layer is very dense, and is continuous in front with the sheath of the masseter and behind with that of the sterno-mastoid, while above it is attached to the zygoma. The deep layer is thin, and is attached above to the periosteum of the auditory meatus and glenoid fossa, and forms the stylo-maxillary ligament, which extends from the tip of the styloid process to the posterior surface of the angle of the jaw, between the insertions of the masseter and pterygoid muscles. The deep surface of the gland sheath is related to the posterior belly of the digastric muscle, the styloid process and muscles rising from it, the external and internal carotid arteries and internal jugular vein, and the ninth, tenth, eleventh, and twelfth nerves. The gland generally sends several processes in different directions. Thus a facial process frequently projects forwards toward the socia parotidis, which latter lies on the masseter above Stenson's duct; cervical and glenoid processes project in the directions indicated by their names ; while a pharyngeal process is of importance, as it passes deeply inwards in front of the styloid process and above the stylo-maxillary ligament toward the pharynx and tonsil. Within the gland are numerous structures, of which the most important are : (a) The external carotid artery, which enters the deep surface of the gland at the junction of the middle and lower third of the posterior border of the ascending ramus of the jaw, passes outwards and backwards from under cover of the ramus, until, on reaching the neck of the condyle, it divides into the internal maxillary and superficial temporal arteries, (b) The facial nerve, which, after leaving the stylo-mastoid foramen, immediately enters the gland and breaks into its branches, crossing superficial to the external carotid artery. The temporo-maxillary vein, the occipital and posterior auricular branches of the external carotid artery, and small branches of the superficial temporal and internal maxillary, a few nerve branches, and lymphatic glands (draining the temporal, scalp region, outer portion of the eyelids, posterior part of the cheek, and ear), are also present in the gland.
Owing to the projecting process of the parotid toward the pharynx, post-pharyngeal abscesses sometimes find their way into the parotid gland ; while, on the other hand, owing to its dense anterior capsule, suppurative processes in the parotid not infrequently extend toward the pharynx. In other cases parotid abscesses point in the temporal or zygomatic fossae or in the neck, while sometimes they burst into the meatus, or even find their way along the divisions of the fifth nerve to the Gasserian ganglion. Parotid abscesses generally arise from septic infection conveyed along the duct from the mouth. Inflammatory conditions of the parotid occasionally supervene on disease or injury to the pelvic viscera, and on some fevers, especially typhoid, while the affection of the gland called 'mumps ' is well known. Owing to the tense capsule, all of these affections are very painful, the auriculo-temporal and great auricular nerves being pressed on, while, where the condition is not relieved by operation, sloughing of the gland may occur, or even ulceration of one of the large vessels, with consequent severe haemorrhage. Movement of the jaw aggravates the pain, altering, as it does, the size and shape of the space. In opening a parotid abscess care is necessary, owing to the important structures contained. A horizontal incision, as low as possible, so as to avoid Stenson's duct and the facial nerve, is generally best, and then, when the capsule is reached, it is penetrated with sinus forceps (Hilton). Penetrating wounds in the parotid region should generally be treated as serious, owing to the various important structures which may be injured. Bleeding in such cases is frequently very severe, and the vessel difficult to get at. Parotid fistula is apt to result from injury to the gland or duct. The most common form of tumour occurring in the parotid is one of a mixed type, and is peculiar in that it generally contains cartilage in addition to fibrous, adenomatous, and myxomatous tissue. Sometimes these tumours are sarcomatous, and rapidly infiltrate the various structures, causing limitation of movement of the jaw, neuralgia, and later anaesthesia and paralysis. They are generally fixed, so that they cannot be moved about in the gland substance, and they sometimes perforate the external auditory meatus. Removal is difficult or impossible. Stenson's duct begins at the anterior margin of the gland by the junction of two main branches proceeding respectively from the upper and lower segments, and runs forwards and slightly downwards to the anterior margin of the masseter, where it bends nearly at right angles, pierces the fatty tissue, buccinator muscle, and mucous membrane of the cheek, and ends by an elliptical orifice on the level of the second upper molar tooth. It is about 2 1/2 inches long and 1/8 inch thick, has a firm feel, by which it may sometimes be detected through the skin, lying about 1/2 inch below the zygoma, and its course may be represented by a line drawn from the lower border of the tragus to a point midway between the nostril and the red margin of the lip. In its course it is accompanied by the transverse facial artery, which lies above it, and infraorbital branches of the facial nerve, which lie above or below it. Wounds of the duct are very apt to lead to salivary fistula, which are treated, where practicable, by establishing an opening between duct and mucous membrane on the proximal side of the fistula. Subcutaneous rupture of the duct leads to extravasation of saliva. Where the duct becomes blocked by calculus a painful retention cyst is apt to develop. In passing a probe it is best to evert the cheek so as to straighten the duct.