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process termed the glenoid lobe is found, passing into the posterior or tympanic part of the glenoid fossa.
Another runs into the interval between the sterno - mastoid and digastric muscles; and a pharyngeal process is occasionally found extending medially, anterior to the styloid process, towards the side of the pharynx.
A pterygoid extension, between the two pterygoid muscles, cannot properly be said to exist.
Embedded in the superficial surface there are usually found several small rounded lymph glands, which can be recognised from the gland tissue by the difference in their colour.
HORIZONTAL SECTION THROUGH MOUTH AND PHARYNX AT THE LEVEL OF THE PALATINE TONSILS.
The facial process of the gland-often of considerable size-is a flat and somewhat triangular portion which runs forwards from the upper part of the front of the gland, and overlaps the masseter muscle to a varying extent; from its most anterior part the parotid duct emerges, and a separated portion of this process, often found lying immediately above the duct, is known as the glandula parotis accessoria (O.T. socia parotidis).
Ductus Parotideus (Stenonis). The parotid duct (O.T. Stenson's) leaves the anterior border of the gland at its most prominent part (Fig. 897). It first runs forwards across the masseter, below the accessory parotid gland, and accompanied by branches of the facial nerve, and the transverse facial artery, which is commonly some distance above, though its relation is variable. Having crossed the masseter, it turns abruptly round the anterior border of this muscle and runs
Embedd glands, whi ressels of t
inwards through the fat of the cheek, practically at right angles to the first part of its course, to reach the buccinator, which it pierces. Then passing for some distance (5 to 10 mm.) between the buccinator and the mucous membrane, it opens into the vestibule of the mouth by a very small orifice, on a variably developed papilla, opposite the crown of the second upper molar tooth.
The course of the duct, which is fairly constant, can be marked on the side of the face by drawing a line from the inferior edge of the acoustic meatus to a point midway between the ala of the nose and the red of the lip; the middle third of this line corresponds fairly accurately, on the surface, to the course pursued by the duct.
The duct measures from 1 to 2 inches (38 to 62 mm.) in length, and inch (3 to 4 mm.) in diameter. The calibre of the duct is very much greater than that of its orifice, which admits only a fine bristle, and for this reason the duct may, to some extent, be looked upon as a reservoir for the saliva, as well as a duct for its conveyance. In the child it pierces the "sucking pad" on its way to the mouth.
A number of vessels and nerves are found in intimate relation to the parotid gland.
These are: (1) The external carotid artery and its two terminal branches. This artery lies at first in a groove in the inferior and deep aspect of the gland. It then enters the gland substance and lies deeply in it, as far up as to the neck of the mandible, when it divides into its two terminal branches. The superficial temporal artery passes onwards and emerges from the superior superficial part of the gland, and the internal maxillary artery turns inwards and emerges from the deep part of the anterior surface.
The transverse facial artery is given off in the substance of the gland, and emerges from it between the zygomatic arch and the duct.
The posterior facial vein descends in the substance of the gland superficially, and divides in it into the two terminal branches which emerge from the inferior part of the gland.
The facial nerve enters the posterior surface of the gland, slightly below its middle, and runs forwards and laterally, dividing into its main branches within the gland, and lying superficial to the external carotid artery and posterior facial vein. Communicating branches from the auriculo-temporal and great auricular nerves to the facial also traverse the gland substance.
Vessels and Nerves.-The arteries which supply the gland arise from the external carotid artery, and from the branches of this artery in relation to the gland.
The veins join the posterior facial vein and its tributaries. The lymph vessels pass to both the superficial and the deep cervical glands; there are also a few small parotid lymph glands, which lie on the surface of the superior and inferior part of the parotid beneath the capsule. Some are said to be embedded in the substance of the parotid itself.
The nerves are derived (a) from the auriculo-temporal, great auricular, and facial, and (b) from the plexus caroticus externus. The fibres of the sympathetic are mainly vaso-constrictor.
The secretory fibres to the gland, arising in the brain-stem, pass out through the glossopharyngeal nerve, and pass from it through the lesser superficial petrosal nerve to the otic ganglion, and from that ganglion to the gland in the auriculo-temporal nerve.
Glandulæ Submaxillares.-The submaxillary glands are next in size to the parotid, and resemble them in their lobulation and colour. Each is placed partly in the submaxillary triangle and partly under cover of the mandible (Fig. 897).
In each gland two portions may be recognised, a somewhat superficial larger part, the body, lying in the submaxillary triangle, and a smaller deep part, the deep process, which springs from the middle of the deep surface of the body.
The superficial part, like the parotid, presents a superficial convex surface, which projects below the mandible, in the submaxillary triangle, but it frequently extends beyond the limits of that space, and overlaps the digastric muscle.
This surface looks downwards and laterally; it is covered by the deep cervical fascia and the platysma and is crossed superficially by the anterior facial vein.
Deep to this surface the body of the gland is wedged upwards, between the medial surface of the mandible and the mylo-hyoid and hyoglossus muscles. It thus presents two surfaces, a lateral, which is in contact with the submaxillary fossa of the mandible, and a medial, related to the mylo-hyoid, hyoglossus, the posterior belly of digastric, and stylo-hyoid muscles.
The deep process passes still further medially, around the posterior free margin of the mylo-hyoid muscle, and comes to lie between the mylo-hyoid and hyoglossus
Embedded in the substance of the gland are found a few submaxillary lymph glands, which are of importance from the connexion they have with the lymph wessels of the lip and of a portion of the tongue.
The external maxillary artery lies embedded in a groove in the superior and posterior part of the gland.
The gland is enclosed in an extremely delicate capsule of connective tissue derived from the deep cervical fascia.
In considering the relations of the gland, it is well to remark that there is in this region a three-sided space bounded laterally by the medial surface of the mandible below the mylo-hyoid line, medially and above by the mylo-hyoid muscle, and below by the skin and fascia passing from the margin of the jaw to the side of the neck. In this space the gland lies with lateral, medial, and inferior surfaces corresponding to the walls of the space.
The posterior end of the gland, which is its most bulky portion, either abuts against, or lies very close to, the sterno-mastoid, and is often overlapped by the inferior end of the parotid gland.
Ductus Submaxillaris.-The submaxillary duct (O.T. Wharton's) leaves the deep surface of the gland about its middle, and runs forwards beneath the mylo-hyoid muscle, along the superior and medial aspect of the deep process of
the gland (Fig. 899). Pursuing its course forwards beneath the floor of the mouth, on the medial side of the sublingual gland, the duct crosses the hyoglossus and the genioglossus muscles, and finally opens on the floor of the mouth at the side of the frenulum linguæ, where its small orifice is placed on the summit of a soft papilla (caruncula sublingualis) close to its fellow of the opposite side.
While running forward beneath the floor of the mouth the duct, which is about two inches long (50 mm.), is crossed by the lingual nerve near the anterior border of the hyoglossus, that is opposite the 2nd molar tooth. The nerve passes from the posterior end of the mylo-hyoid ridge (against which it lies) forwards and medially in order to reach the inferior surface of the tongue, and it passes below the duct at the point indicated. As in the case of the parotid duct, the calibre of the submaxillary duct is much greater than that of the orifice by which it opens; for this reason it likewise may be looked upon as forming, to some extent, a reservoir for the saliva secreted by the gland.
Vessels and Nerves.-The arteries come chiefly from the external maxillary artery and its submental branch: the veins accompany the arteries. The nerves are derived through the submaxillary ganglion (which lies above the deep process of the gland), from the chorda tympani and lingual, and from the sympathetic plexus around the external maxillary artery. The lymph vessels pass to the submaxillary lymph glands.
Glandulæ Sublinguales.-The sublingual glands, the smallest of the principal salivary glands, are situated more deeply than the others.
Each lies immediately below the mucous membrane of the floor of the mouth, between the tongue and the gum of the mandible, and there it causes the elevation on the floor of the mouth termed the plica sublingualis.
When the mucous membrane is removed from this region, the gland is found to be lying in the interval between the sublingual fossa (on the inner surface of the mandible above the mylo-hyoid line) and the genioglossus muscle, which passes from the mandible to the tongue. Below, it rests upon the deep surface of the mylo-hyoid muscle.
In shape it is almond-like, flattened from side to side, but is much wider (from above downwards) anteriorly than posteriorly. It is usually from 1 to 1 inches (37 to 45 mm.) in length, whilst its bulk is about equal to that of two or three almonds.
Its detailed relations are as follows:-Its lateral surface rests against the inner aspect 1. of the body of the mandible above the mylo-hyoid line. Its medial surface is in contact with the genioglossus, styloglossus, and hyoglossus muscles, as well as with the submaxillary
A. Section of human submaxillary gland x 400.
B. Section of human parotid gland x 400.
duct, which runs forwards between the gland and the muscles. Below, it rests on the mylo-hyoid, and at its posterior part on the deep process of the submaxillary gland; whilst its upper prominent border is covered only by the mucous membrane of the mouth, here raised up by the gland to form the plica sublingualis (Fig. 892). The anterior portion of the gland is much deeper and more bulky than the posterior half, and it meets its fellow in the median plane beneath the frenulum linguæ. The posterior extremity grows gradually more slender, but may extend to the posterior part of the mylo-hyoid ridge, where it lies above the deep process of the submaxillary gland.
Its ducts, generally known as the ductus sublinguales minores (O.T. ducts of Rivinus), are about twelve in number and of small size; they leave the superior part of the gland, and, after a short course, open on a series of papillæ, visible to the naked eye, which are placed along the summit of the plica sublingualis.
The gland is not enclosed in a distinct capsule, thus differing from the parotid and submaxillary glands; but its numerous lobules, which are smaller than those of the glands just mentioned, are held together by fine connective tissue, loosely, but still in such a manner as to make one more or less consolidated mass out of what was, in the embryo, a number of separate glands.
As a rule all the ducts open separately on the summit of the plica sublingualis, and apparently none of them join the submaxillary duct. Frequently some of those from the anterior and more bulky part of the gland are larger than the others, but the presence of a large duct running alongside of the submaxillary duct, and opening with or beside it, ductus sublingualis
major (O.T. duct of Bartholin), is very rare, and must be considered as an exceptional condition in man, although normal in the ox, sheep, and goat. The same may also be said of ducts from the sublingual, which are described as opening into the submaxillary duct.
Vessels and Nerves.-The arteries are derived from the sublingual artery, a branch of the lingual, and from the submental, a branch of the external maxillary. The nerves come from the lingual, chorda tympani, and the external maxillary plexus, through a branch of the submaxillary ganglion which joins the lingual, and is conveyed by it to the gland. secretory fibres run in the chorda tympani nerve, and thence through the submaxillary ganglion to the gland.
The glandula lingualis anterior (Blandini, Nuhni) has been described with the tongue.
Structure of the Salivary Glands (Fig. 900).—Each of the principal salivary glands consists of a number of lobules, loosely united together by connective tissue. From each of them one or more ducts emerge. Each duct when traced onwards divides into branches, which terminate in a group of saccular or tubular alveoli.
The epithelium lining the ducts is columnar in character, but becomes flattened at the junction with the alveoli.
The epithelium lining the alveoli shows different characters in different glands. In the parotid, and the small salivary glands of the vallate papillæ in which the secretion is watery or albuminous, the cells are uniform in character, and of small size. When the gland is at rest, the cells are filled with small granules, which when the secretion is poured out are transformed into the gland ferment (ptyalin). After secretion, only the deeper parts of the cells show the presence of granules. The nuclei are rounded, and lie near the centre of the cells. In the sublingual, labial, buccal, and other glands of the mouth and palate the secretion is of a mucous character and the cells are larger, and the nuclei are placed deeply. The cells appear clear and swollen unless special methods of preparation are employed. In such cases, e.g., when examined in serum, the cells are seen to contain large and distinct granules of mucigen which in secretion are transformed into mucus.
In the submaxillary gland and the anterior lingual gland both varieties of cells are present. In these cases, the larger, clear mucous cells line the cavity of the alveolus, and the smaller granular serous cells are arranged upon the basement membrane, deep to the former cells, in crescentic masses, termed the crescents or demilunes of Gianuzzi. They communicate with the cavity of the alveolus by small channels between adjacent mucous cells.
After secretion, the mucous cells become smaller, and stain more deeply than when loaded with mucigen before secretion.
The pharynx is the expanded upper portion of the alimentary canal which lies posterior to and communicates with the mouth, the larynx, and the nasal cavities, and is continuous inferiorly with the superior end of the esophagus or gullet (Fig. 901).
It extends from the base of the skull, above, to the level of the sixth cervical vertebra (Fig. 903) and the lower border of the cricoid cartilage, below.
Its total length varies from 5 to 5 inches (12.5 to 140 cm.).
The inferior portion alone, that is, the parts lying opposite and inferior to the opening of the mouth, is functionally a part of the alimentary canal, for the portion above the level of the soft palate is used for respiration only. It is, however, convenient to study the structure and relations of the whole of the pharynx at once.
Structurally the pharynx is a fibro-muscular bag, of conical form, wide above and narrow below. The wall of the superior part of the pharynx, in the region of the base of the skull, is firmly attached to the surrounding bony structures, especially around the orifice of the choanæ, and hence in this superior portion of the pharynx there is a permanent cavity containing air.
The lower portion gradually assumes a more tubular form, and the anterior and posterior walls approach one another, so that below the level of the opening of the larynx they are in contact with one another, and the cavity is reduced to a slit, except during the passage of food.
Dimensions of the Pharynx.-From the fornix pharyngis, i.e. the highest part of the roof, to the superior surface of the soft palate at its junction with the hard palate, measures about inches, or 3 cm. The vertical extent of the oral part of the pharynx is about 2 inches, or 6 cm., and that of the laryngeal part is about 23 inches, or 7 cm.
The inferior end of the pharynx is usually about 5 to 6 inches from the margins of the incisor tooth, in a line passing through the cavities of the mouth and of the oral and laryngeal parts of the pharynx.
The other diameters are as follows: the antero-posterior diameter (depth) of the superior