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glossus muscle, to the upper deep cervical lymph glands, especially to some glands near the bifurcation of the common carotid artery. From the posterior part of the tongue the lymphvessels pass laterally on each side below the palatine tonsil, and thence follow the course of the tonsillar lymph-vessels to the upper deep cervical lymph glands. Some central vessels, from the median portion of the tongue, pass downwards to the submaxillary glands, and also to the upper deep cervical glands, on the lateral side of the internal jugular vein.
Nerves.-The nerves which supply the tongue are: (1) The hypoglossal nerve, the motor nerve of the tongue, which enters the genioglossus and passes up in its substance to the intrinsic muscles, in which it ends. (2) The lingual nerve, a branch of the mandibular nerve, which is accompanied by the chorda tympani branch of the facial nerve. The lingual, after crossing the hyoglossus, breaks up and enters the longitudinalis inferior and genioglossus muscles, and thus makes its way upwards to the mucous membrane of the anterior two-thirds of the tongue-the lingual itself conferring common sensation on this part, the chorda tympani probably carrying to it taste fibres. (3) The glosso-pharyngeal nerve passes forwards beneath the upper part of the hyoglossus muscle, and sends its terminal branches to the mucous membrane of the posterior third of the tongue, supplying the papillæ vallatæ, and the part of the tongue behind these, with both gustatory and common sensory fibres. (4) The internal laryngeal nerve also distributes a few fibres to the posterior part of the base of the tongue, near the epiglottis.
Numerous organs, differing widely in structure, function, and development, are commonly included under the term glands. It may indicate any of the following
(1) Glands producing a visible fluid or semi-fluid secretion, which is discharged from the cells of the gland, either directly or by a duct, on to a free surface, where it is useful chemically or mechanically, or by which it is drained away. Glands of this type connected with the alimentary canal are serous and mucous glands, salivary glands, gastric and intestinal glands, and the liver and pancreas.
(2) The so-called ductless glands, which possess no ducts, but secrete some substances, which are directly and gradually transmitted from the cells of the gland to the blood or lymph stream, and are of use in the general metabolism of the body. Such structures are the thyreoid gland, the suprarenal glands, the parathyreoids, and the hypophysis cerebri.
(3) Cytogenic or cell-producing glands, not always epithelial, and usually with no distinct duct, consist of aggregations of special cells, enclosed in a more or less definite framework of connective tissue, freely supplied with blood- and lymph-vessels. Glands of this type are concerned in the production, from the cells in the glands, of special cells, which are liberated from the gland tissue, and pass away from it. Such glands are lymph glands, the bone marrow, and the reproductive glands-testes and ovaries.
In structure they present wide differences.
Glands may also be classified according to their development, and on this basis the following groups are recognised :
(1) Glandulæ epitheliales, developed from epithelial cells. These may (a) possess a duct, in which case they are termed glandulæ evehentes; or (b) they may be constituted as ductless glands, and they are then termed glandulæ clausæ. To this last group belong the thyreoid gland, the hypophysis, and the suprarenal glands.
(2) Glandulæ vasculares, developed in connexion with vessels, and not containing epithelial cells. This group includes all the lymph glands, the lymph nodules found in the intestine, the tonsils, the thymus, and the spleen.
In the following paragraphs only the true glands of the alimentary system -namely, the glands of epithelial origin, characterised by the possession of ducts -are considered.
Such glands may be defined as epithelial organs used for the secretion or excretion of some particular substance or substances from the body. They usually consist of a number of cells, and there may be different kinds of cells in a gland.
The simplest form of this type of gland is a portion of an epithelial surface, continuous with adjacent portions of the surface, but involuted from the surface to which it originally belonged.
The simplest form in which this involution occurs is as a single pocket, of uniform size throughout, forming a simple tubular gland. Of this kind are the intestinal glands in the wall of the small intestine.
In other cases there may be a bag-like enlargement of the end of the gland, forming a sort of pocket, called an alveolus (alveolus, small stomach or bag), and this type of gland is known as the simple alveolar gland. It does not exist in the alimentary canal.
In some cases the lower part or fundus of the gland does all the secretion, and the upper part forms a tube or duct that carries the secretion to the surface.
When the outgrowth forming the gland remains undivided, the gland is known as a simple gland. It may, on the other hand, break up into two or more branches, and it then is known as a compound gland, and this compound gland may be tubular, alveolar, or of a mixed tubular and alveolar form.
When the fundus of the gland at the extremities of the ducts becomes a highly differentiated saccular region, consisting of several enlargements (alveoli) at the end of a duct, it is called an acinus (äkivos, a grape, or grape-stone), from the fancied resemblance it presents to a cluster of grapes at the end of a stalk. A gland formed of several such structures collected together is often called a compound acinous or racemose gland (racemus, a cluster).
Small duct from an alveolus
An alveolus with secreting cell
Most of the glands of
FIG. 895.-SECTION OF A SEROUS GLAND ON THE LEFT, A MUCOUS GLAND tongue, pharynx, so-
A compound acinous
branches more or less freely according to the size of the gland. The terminal divisions of the
The foregoing may be summarised in tabular form thus:
I. Simple glands.-Duct undivided.
(a) Simple tubular (undilated at end)-e.g. intestinal glands and certain gastric glands.
II. Compound glands.-Duct divided.
(a) Compound tubular, branched elongated tubes, no acini-e.g. most gastric glands.
1 Some authorities consider the duodenal glands of Brunner to belong to the class of compound tubular glands (Heidenhain, Watney, Jonnesco, etc.).
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(c) Acino-tubular, branched duct, with elongated narrow acini on terminal branchese.g., pancreas, duodenal glands.
General Structure of Glands.-Whilst the small glands, such as those of the mouth and pharynx, are placed in the mucosa or submucosa close to the point at which their ducts open on the surface, the large glands forming distinct masses, often lie at a considerable distance from the points at which their ducts open, and are generally surrounded by special capsules.
Each of these large glands of the acinous type, such as the parotid or submaxillary, presents the following general arrangement. The gland is made up, as can be seen with the unaided eye, of a number of masses, often as large as peas, which are surrounded and held together by connective tissue. These are known as lobes, and to each a branch of the duct passes. The lobes are in turn made up of a number of smaller masses-lobules -each having a special branch of the lobar duct. These again are composed of smaller lobules, and so on to a varying degree. Finally, the smallest are made up of a terminal branch of the duct, with a cluster of acini or alveoli developed upon it.
The acini or alveoli, the special secreting portions of the gland, are composed of a basement membrane, often fenestrated or basket-like, formed of flattened cells, on the outer side of which the blood- and lymph-vessels lie. The inner surface of this membrane is lined by the secreting epithelial cells, usually polygonal in shape, which almost completely fill the alveolus. A small lumen, however, is left, into which the secretion of the cells is shed; thence it passes into the duct of the lobule, and thus to the main duct.
The blood- and lymph-vessels, on entering the gland, break up and run, branching as they go, in the connective tissue which conveys them to all parts of the gland.
Salivary Glands. This term is generally understood to include only the three large masses of glandular tissue found on each side of the face and upper part of the neck-namely, the parotid, submaxillary, and sublingual glands. But, as previously pointed out, numerous other small glands of a similar nature are found in the lips, cheeks, palate, tongue, etc. These have already been sufficiently described, and require no further mention.
Glandula Parotis. The parotid gland is the largest of the salivary glands, and lies on the side of the face, below and in front of the ear, and is prolonged inwards deeply from the surface.
It forms a lobulated mass, of a yellowish or light reddish-brown colour, with a large triangular superficial surface. From this mass a process of the gland passes medially posterior to the upper part of the ramus of the mandible below the base of the skull almost to the side wall of the pharynx. It is known as the
The superficial surface extends upwards nearly to the zygoma, and downwards as far as to the angle of the mandible. It is prolonged anteriorly on the superficial surface of the masseter muscle in the form of a process, often triangular in shape, called the facial process, while at the back it comes into contact with the external acoustic meatus, the front of the sterno-mastoid muscle, and the mastoid process.
Processus Retromandibularis.-This portion of the gland occupies a deep fossa, called the parotid fossa, of considerable size, which has two nearly vertical sides, an anterior and posterior. These sides converge towards one another and meet deeply, and so form the apex of the fossa. This fact is well brought out by a horizontal section through the head about the middle of the gland (Fig. 896).
From this it will be seen that the posterior wall of the fossa is formed, medial to the sterno-mastoid muscle, by the posterior belly of the digastric and the stylohyoid muscles, with the occipital artery, and more deeply still, by the root of the styloid process and the carotid sheath and its contents, and especially by the internal jugular vein, separating the gland from the vertebral column.
The anterior wall of the fossa is formed by the ramus of the mandible and the masseter and internal pterygoid muscles.
Fascia Parotideomasseterica.—The parotid recess is covered over on the one hand,
and lined on the other, by fascia. The covering layer is specially known as the fascia parotideomasseterica (O.T. parotid fascia) and both it and the lining layer are derived from the deep cervical fascia, which divides to enclose the gland. The parotideo-masseteric fascia is connected, on the surface, above to the zygoma; posteriorly, to the acoustic meatus and anterior border of the sterno-mastoid; below, it is continuous with the deep cervical fascia, and anteriorly it passes over the masseter, and blends with the fascia buccopharyngea. The fascia forms a lining for the recess, and is united above to the periosteum over the acoustic meatus and posterior part of the glenoid fossa; medially it is
FIG. 896.-HORIZONTAL SECTION THROUGH MOUTH AND PHARYNX AT THE LEVEL OF THE PALATINE TONSILS The stylopharyngeus, which is shown immediately to the medial side of the external carotid artery, and the prevertebral muscles, are not indicated by reference lines.
connected to the styloid process; whilst below it joins the deep cervical fascia. Taken together, the two layers form a definite capsule which completely encloses the gland. In connexion with the lower and anterior part of this capsule is developed a special flat band, the stylo-mandibular ligament, which passes downwards and laterally from the styloid process to the angle of the mandible. It separates the anterior part of the parotid gland from the posterior border of the internal pterygoid muscle; perhaps occasionally, also, from the upper and posterior part of the submaxillary gland.
Shape and Relations of the Parotid Gland.-The main mass of the parotid gland is three-sided (Fig. 896), the three surfaces being superficial, anterior, and posterior.
Superficial Surface. This surface is somewhat triangular in form, though irregular in outline. Its long posterior border lies in front of the external acoustic meatus, and the sterno-mastoid muscle. Its superior border lies below the zygomatic arch, and the inferior border passes irregularly upwards and anteriorly to
join it. The apex, directed anteriorly, is formed by the facial process of the gland, and lies on the masseter muscle, and the duct of the gland issues from it, or just below it.
This superficial surface is frequently prolonged beyond the limits of the parotid fossa, and passes downwards over the digastric muscle. It may descend beyond the angle of the mandible, and come into immediate relation with the posterior part of the submaxillary gland, from which it is separated merely by a thin layer of the deep cervical fascia.
Deep Portion of the Gland.-This portion of the gland presents an anterior surface looking forwards, deeply concave, and a posterior surface, irregular in outline, directed backwards and medially.
These surfaces meet medially at the medial border, which may lie so deeply as to be in contact with the side wall of the pharynx. The lower part of the styloid
process in many cases lies in contact with the inferior part of this border, and in such cases the process, together with the styloglossus and stylopharyngeus muscles, separates the medial border from the pharynx. The superior and inferior borders, at the union of the anterior and posterior surfaces, are irregular in outline, and indefinite.
The relations of these two surfaces are as follows:
The anterior surface is wrapped round the ramus of the mandible, and extends on to the muscles which cover this portion of the bone laterally and medially, that is, on to the masseter and internal pterygoid muscles respectively.
The posterior surface, in contact with the posterior wall of the fossa, is moulded upon the structures which form that wall. It is in contact, from the surface medially, with the sterno - mastoid muscle, the mastoid process, the external acoustic meatus, the posterior belly of the digastric muscle, the internal jugular vein, and the root of the styloid process and the styloid muscles. It is often deeply grooved by the posterior belly of the digastric.
The posterior surface is occasionally prolonged medially beyond the lower portion of the styloid process, towards the pharynx. In such cases, the lower part of the styloid process lies in a groove on the posterior surface of the gland, and is not in contact with its medial border as described above.
The gland frequently gives off processes which pass into the intervals between the structures bounding the fossa. Occasionally from its superior end a small