Its outer surface is convex and lobulated, and is covered by the skin and fascia, and partially by the platysma muscle. It is bounded above by the zygoma, below by a line drawn backwards from the lower border of the jaw to the sterno-mastoid muscle, and behind by the external meatus of the ear, the mastoid process, and sterno-mastoid muscle. Its anterior border, which lies over the ramus of the lower jaw, is less distinctly defined, and stretches forwards to a variable extent on the masseter muscle. It is from this anterior border of the gland that the excretory duct passes off; and there is

Fig. 572.-SKETCH OF A SUPERFICIAL DISSECTION OF THE FACE, SHOWING THE POSITION OF THE PAROTID AND SUBMAXILLARY GLANDS.

p, the larger part of the parotid gland; p", the small part, which lies alongside the duct on the masseter muscle; d, the duct of Stenson before it perforates the buccinator muscle; a, transverse facial artery; n, n, branches of the facial nerve emerging from below the gland; f, the facial artery passing out of a groove in the submaxillary gland and ascending on the face; sm, superficial larger portion of the submaxillary gland lying over the posterior part of the mylo-hyoid muscle.

frequently found in connection with the duct, and lying upon the masseter muscle, a small process or a separated portion of the gland, which is called glandula socia (socia parotidis). On trying to raise the deeper part of the parotid gland from its position, it is found to extend far inwards, between the mastoid process and the ramus of the jaw, towards the base of the skull, and to be intimately connected with several deep-seated parts. Thus, above, it reaches into and occupies the posterior part of the glenoid cavity; behind and below, it touches the digastric muscle, and rests on the styloid

process and styloid muscles; and, in front, under cover of the ramus of the jaw, it advances a certain distance between the external and internal pterygoid muscles.

The internal carotid artery and internal jugular vein are close to the deep surface of the gland. The external carotid artery, accompanied by the temporal and internal maxillary veins, passes through the parotid gland; and in that situation arise the temporal and internal maxillary arteries, as also the auricular and transverse facial branches of the temporal. The gland is also traversed by the facial nerve, which divides into branches within its substance, and it is pierced by branches of the great auricular nerve.

The parotid duct, named also Stenson's duct (d. Stenonianus), appears at the anterior border of the gland, about one finger's breadth below the zygoma, and runs forwards over the masseter muscle, accompanied by the socia parotidis, when that accessory portion of the gland exists, and receiving its ducts. At the anterior border of the masseter, the duct turns inwards through the fat of the cheek and pierces the buccinator muscle; and then, after running for a short distance obliquely forwards beneath the mucous membrane, opens upon the inner surface of the cheek, by a small orifice opposite the crown of the second molar tooth of the upper jaw. Its direction across the face may be indicated by a line drawn from the lower margin of the concha of the ear to a point midway between the red margin of the lip and the ala of the nose. The length of the Stenonian duct is about two inches and a half, and its thickness about one line and a half. At the place where it perforates the buccinator, its canal is as large as a crow-quill, but at its orifice it is smaller than in any other part, and will only admit a very fine probe. The duct is surrounded by areolar tissue, and consists of an external, dense, and thick fibrous coat, in which contractile fibres are described, and of an internal mucous tunic, which is continuous with that of the mouth, but which is covered, from the orifice of the duct as far as to the smallest branches, with a columnar epithelium.

The parotid gland belongs to the class of compound racemose glands, and consists of numerous flattened lobes, held together by the ducts and vessels, and by a dense areolar web, which is continuous with the fascia upon its outer surface; but the gland has no special or proper coat. The lobes are again divided into lobules, each of which consists of the branched terminations of the duct, and of vessels, nerves, and fine areolar tissue. The ducts terminate in closed vesicular extremities, about th of an inch or more in diameter, which are lined with epithelium, and have capillary vessels ramifying upon them.

The vessels of the parotid gland enter and leave it at numerous points. The arteries are derived directly from the external carotid, and from those of its branches which pass through or near the gland. The veins correspond. The absorbents join the deep and superficial set in the neck; and there are often one or more lymphatic glands imbedded in the substance of the parotid. The nerves come from the sympathetic (carotid plexus), and also, it is said, from the facial and the superficial temporal and great auricular nerves.

An instance is recorded by Gruber of a remarkable displacement of the parotid on one side; the whole gland being situated on the masseter muscle as if it were an enlarged socia parotidis. (Virchow's Archiv, xxxii., p. 328.)

The Submaxillary Gland.

The submaxillary gland, the next in size to the parotid gland, is of a spheroidal form, and weighs about 2 or 21 drachms. It is situated imme

THE SUBLINGUAL GLAND.

817

diately below the base and the inner surface of the inferior maxilla, and above the digastric muscle. In this position it is covered by the skin and the platysma myoides, and its inner surface rests on the mylo-hyoid, hyo-glossus, and stylo-glossus muscles; above, it corresponds with a depression on the inner surface of the jaw-bone; and it is separated behind from the parotid gland merely by the stylo-maxillary membrane. The facial artery, before it mounts over the jaw-bone, lies in a deep groove upon the back part and upper border of the gland.

The duct of the submaxillary gland, named Wharton's duct, which is about two inches in length, passes off from the gland, together with a thin process of the glandular substance, round the posterior border of the mylohyoid muscle, and then runs forwards and inwards above that muscle, between it and the hyo-glossus and genio-hyo-glossus, and beneath the sublingual gland, to reach the side of the frænum linguæ. Here it terminates, close to the duct of the opposite side, by a narrow orifice, which opens at the summit of a soft papilla seen beneath the tongue. The structure of this gland is like that of the parotid; but its lobes are larger, its surrounding areolar web is finer, and its attachments are not so firm. Moreover, its duct has much thinner coats than the parotid duct.

The blood vessels of the submaxillary gland are branches of the facial and lingual arteries and veins. The nerves include those derived from the small submaxillary ganglion, as well as branches from the mylo-hyoid division of the inferior dental nerve, and the sympathetic.

The Sublingual Gland.

The sublingual gland, the smallest of the salivary glands, is of a narrow oblong shape and weighs scarcely one drachm. It is situated along the

Fig. 573.-VIEW OF THE RIGHT SUB-
MAXILLARY AND SUBLINGUAL GLANDS
FROM THE INSIDE.

A part of the right side of the jaw, divided from the left at the symphysis, remains; the tongue and its muscles have been removed; but the mucous membrane of the right side is retained and is drawn upwards so as to expose the sublingual glands. 8 m, the larger superficial part of the submaxillary gland; f, the facial artery passing through it; sm', deep portion prolonged within the mylo-hyoid muscle mh; sl, is placed below the anterior large part of the sublingual glands, with the duct of Bartholin partly shown;

sl, placed above the hinder small end of the chain of glands, indicates the ducts of one or two perforating the mucous membrane; d, the papilla, at which the duct of Wharton opens in front behind the incisor teeth; d', the commencement of the duct; h, the hyoid bone; n, the gustatory nerve.

floor of the mouth, where it forms a ridge between the tongue and the gums of the lower jaw, covered only by the mucous membrane. It reaches from the frænum linguæ, in front, where it is in contact with the gland of the opposite side, obliquely backwards and outwards for rather more than an inch and a half, On its inner side it rests on the genio-hyo-glossus ; beneath, it is supported by the mylo-hyoid muscle, which is interposed

between it and the submaxillary gland; but it is here in close contact with the Whartonian duct, with the accompanying deep portion of the last-named gland, and also with the lingual nerve.

The lobules of the sublingual gland are not so closely united together as those of the other salivary glands, and the ducts from many of them open separately into the mouth, along the ridge which indicates the posi

Fig. 574.-SKETCHES ILLUSTRATING THE FORMATION OF THE PAROTID GLAND (from J. Müller).

A, head of a foetal sheep magnified, showing the early simple condition of the parotid gland with the duct injected.

B, parotid gland of a foetal sheep more advanced, the ducts and blood-vessels injected.

tion of the gland. These ducts, named ducts of Rivini, are from eight to twenty in number. Some of them open into the duct of Wharton. One, longer than the rest (which is occasionally derived in part also from the submaxillary gland), runs along the Whartonian duct, and opens either with it or very near it; this has been named the duct of Bartholin.

The blood-vessels of this gland are supplied by the sublingual and submental arteries and veins. The nerves are numerous, and are derived from the lingual branch of the fifth pair.

Saliva. The saliva is a clear limpid fluid, containing a few microscopic granular corpuscles. Its specific gravity is from 1.006 to 1.008, and it has only from 1 to 14 parts of solid matter in 100. The saliva is always alkaline during the act of mastication; but the fluid of the mouth becomes acid, and remains so until the next time of taking food: the reason being that the secretion of the mucous follicles of the mouth is acid, while that of the salivary glands is alkaline. Its chief ingredients, besides water and mucus, are a peculiar animal extractive substance, named salivine, with some alkaline and earthy salts. It is remarkable, besides, for containing a minute proportion of sulphocyanide of potassium.

Development.-In mammalia, according to Müller and Weber, the salivary glands as shown in the case of the parotid gland in the embryo of the sheep, first appear in the form of a simple canal with bud-like processes lying in a blastema, and communicating with the cavity of the mouth. This canal becomes more and more ramified to form the ducts, whilst the blastema soon acquires a lobulated form, corresponding with that of the future gland, and at last wholly disappears, leaving the branched ducts, with their blood-vessels and connecting tissues. The submaxillary gland is said to be the first formed; then the sublingual and the parotid.

THE PHARYNX.

The pharynx is that part of the alimentary canal which unites the cavities of the mouth and nose to the oesophagus. It extends from the base of the skull to the lower border of the cricoid cartilage, and forms a sac open at the lower end, and imperfect in front, where it presents apertures leading into the nose, mouth, and larynx.

The velum pendulum palati projects backwards into the pharynx, and during the passage of the food completely separates an upper from a lower part by means of the contraction of the muscles connected with it which are placed in the posterior pillars of the fauces. Seven openings lead into the cavity of the pharynx; viz., above the velum, the two posterior openings of the nares and, at the sides, the apertures of the Eustachian tubes; while below the velum, there is first the passage leading from the mouth, then the superior opening of the larynx, and lastly the passage into the œsophagus. The walls of the pharynx consist of a fascia or layer of fibrous tissues, named the pharyngeal aponeurosis, dense at its upper part but lax and weak below, surrounded by muscles, and lined by a mucous membrane. At its upper end this fibrous wall is attached to the posterior margin of the body of the sphenoid bone, and passes outwards to the petrous portion of the temporal. It is strengthened in the middle line by a strong band descending between the recti antici muscles from a part of the basilar process which often presents a marked tubercle.

The pharynx is usually described as attached superiorly to the basilar process of the occipital bone; it is certain, however, from dissections in both young and old subjects, that the recti capitis antici muscles come quite forward to the anterior extremity of the basilar process; that the posterior wall of the pharynx at its upper end forms a cul-de-sac on each side opposite the tip of the petrous bone, and lies in a curve, with its convexity forwards, in front of the recti muscles; and that the only connection of the pharynx with the occipital bone is by means of the mesial band, which has been described, and which forms a cranio-pharyngeal ligament. The tubercle from which this band principally springs is sometimes named tuberculum pharyngeum.

Behind, the wall of the pharynx is loosely connected by areolar tissue to the prevertebral fascia covering the bodies of the cervical vertebræ and the muscles which rest upon them. At the sides, the walls have similar connections, by loose areolar tissue, with the styloid process and its muscles, and with the large vessels and nerves of the neck. In front, they are attached in succession to the sides of the posterior nares, the mouth, and the larynx. Thus, commencing above by a tendinous structure only, at the petrous portion of the temporal bone and the Eustachian tube, the walls are connected by means of muscle and fibrous membrane, first, with the internal pterygoid plate, then with the pterygo-maxillary ligament, and next with the mylo-hyoid ridge of the lower jaw; below this, they are attached