GLAND. 481 tended by these writers that the last named bodies elaborate from the blood certain fluids, and that as far as the real function of a gland is concerned, it matters not whether the secreted fluid escapes by a proper excretory duct, or is taken up by the lymphatic vessels; it is, in deed, supposed by Haase that these bodies, like the true glands, possess excretory ducts, but this opinion has received little support.
This method of viewing the subject appears to be very injudicious ; because it is based on the assumption that certain organs secrete fluids from the blood, but of which secretion we have no evidence ; and further, because organs are classed together, between which there is no similarity either of structure or of function.
In establishing a well-founded distinction between parts which, in their general form and outward appearance, bear a resemblance to each other, it is proper to seek for some lead ing and obvious character, concerning which there can be no dispute. In applying this rule to the present case, we shall find that the spe cial distinction of a true gland, as contrasted with those organs with which it has been assi milated, is the possession of an excretory canal or duct ; and taking this as the essential cha racteristic, there is no difficulty in perceiving that the glandular system in the human body ought to be restricted to the following parts:— Mucous glands, comprising, a, simple mu cous glands or follicles, dispersed over the whole extent of the various mucous surfaces, either insulated or collected together, as the glandulm l'eyeri scu ag,gregatm. b, Compound mucous glands, (g. agglutinatm,) formed of the preceding, collected into masses, and slightly modified in their structure, comprising the molar, labial, palatine, and buccal glands, the lachrymal caruncle, tonsils, Cowper's glands, prostate, and seminal vesicles. c, Sebaceous glands, consisting of those of the skin, the ceruminous glands, the Meibomian glands. d, Conglomerate glands, (g. conglomeratm ;) these, which are the most complex of the glan dular organs, consisting of the salivary glands and pancreas, the mammary glands, the testicle, the kidney, and the liver.
These glands may be classed according to their functions in the economy as follows:— I. For lubrication and protection; a. mu cous glands in all parts of the body ; b. seba ceous glands ; c. lachrymal gland ; d. lachry mal caruncle.
II. Connected with digestion ; a. salivary gland ; b. pancreas ; c. liver.
Ill. Connected with generation ; a. testis ; b. prostate ; c. seminal vesicles ; d. Cowper's glands; e. mammary gland.
IV. For excretion ; a. kidney ; b. liver.
By extending the principle that all glands are in reality nothing but processes of the mucous mem brane ending in cul-de-sac, the lungs have, by some writers, been included amongst the glandular organs, the trachea, it is said, performing the office of an excretory duct. It is certain, as we shall subsequently show, that the lungs present, both in their formation and functions, a close approxima tion to the true glands.
VUL.
The particular description of the above organs and the modifications of the general glandular structure they present, will be found in the articles KIDNEY, LACIIRYMAL APPARA TUS, MAMMA, &C.
Situation.—The principal glands are placed in the head and abdomen ; in the extremities, with the exception of those of the skin, they are totally absent. In general they are pro tected from external injury by being lodged deeply in the cavities of the body ; but to this rule there are several important exceptions, as the mammy, testes, parotid glands, &c.
Organization.—I n the whole range of Ana tomy, whether Human or Comparative, there are probably no organs which, on account of the complexity of their structure, the number and variety of forms which they present, and the importance of their functions in the animal kingdom, are more interesting than the glands, or the structure of which, until within a very recent period, was more imperfectly understood. Even at the present time the prevailing ideas respecting the essential characters of the glan dular organization are in general so vague and indefinite, and but too often positively errone ous, that I feel myself called upon to enter more fully into the investigation of this subject, than would otherwise be necessary. Much of this uncertainty has arisen from the fact that, whilst the views of the immortal Malpighi, founded as they are on truly philosophic grounds, have never attracted that investigation to which they are so justly entitled, the theore tical opinions of ltuysch, being received with all the eclat inspired by his unrivalled skill in vascular injections, have been generally adopted. It is true that, on many minor points, Malpighi was in error; and that the vagueness of his descriptions, and his infelicitous comparison of the ultimate divisions of the glands with clus ters of grapes or acini,' greatly assisted in pre venting his opinions being generally admitted or even comprehended. But those distin guished anatomists who have, by their recent inquiries, at length decided the long-disputed theories of Malpighi and Ruysch, have proved that in all essential points the conclusions of the former great authority are founded in truth.
.illinute structure. —The investigation into the structure of the glands, when conducted in accordance with the enlightened principles of philosophical anatomy, shows that the laws which regulate their formation are simple and definite ; and that, although Nature has dis played here, as in all her other works, immense fertility in modifying the forms and characters of the several glands, so as to render them effi cient to the performance of their varied offices, yet in no single instance is there a departure from that structure, which constitutes the type of the whole glandular system. The unifor • This term, so much employed in descriptions of the glands, yet so indefinite in its acceptation, has caused such confusion and misconception, that it is most desirable to abolish it from the nomen clature of Anatomy. In the descriptive part of the present article, I shalt therefore scrupulously avoid employing this expression.
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