1. THE ANIMAL KINGDOM, CONSIDERED ANATOMICALLY, PHYSICALLY, AND PHILOSOPHICALLY.

PART I. THE VISCERA OF THE ABDOMEN, OR THE ORGANS OF THE INFERIOR REGION.

PROLOGUE.

NOTHING whatever is more to be desired, or more delightful than the light of truth; for it is the source of wisdom. When the mind is harassed with obscurity, distracted by doubts, rendered torpid or saddened by ignorance or falsities, and truth emerges as from a dark abyss, it shines forth instantaneously, like the sun dispersing mists and vapors, or like the dawn repelling the shades of darkness. For truths in the intellect or rational mind are analogous to lights and rays in ocular vision; falsities that have the appearance of truth are analogous to unreal or phosphoric lights; doubts, to clouds and shadows; and ignorance itself is thick darkness and the image of night: thus one thing is represented in another.

430. CHAPTER VI. THE THYMUS GLAND.

HEISTER. "The thymus is a gland of considerable size in new-born infants, situated in the upper part of the thorax, close behind the sternum, and lying upon the pericardium, and the trunks of the aorta and superior vena cave. It extends from the pericardium, along the trunk of the aorta, to the origin of the carotid arteries, and in some instances I have found it ascend nearly as high as the thyroid gland. It is of an uncertain, variable, or irregular figure; and in infants, of a pale, fleshy color, but of a more dusky hue in adults. Its size is greatest in infancy, when it is about three inches long, two inches broad, and an inch and a half thick: it decreases gradually during childhood, and almost entirely disappears in adults and old persons. It is of a glandular, conglomerate structure, and is surrounded by a membrane. Its blood-vessels come at one time from either the subclavian, mammary, or mediastinal vessels; at another time, from the carotids and the jugulars. Its lymphatics run sometimes to the thoracic duct, at other times to the subclavian vein, and generally speaking, have no valves. (Comp. Anat., n. 256.) J. I. Mayer cites from J. de Muralto (Observ. xxxii), that the latter saw a great number of crystalline vessels in the thymus, winding to the mediastinum and pericardium; and also a firm membranous duct, running from this gland to the tonsils. (Ibid., not. 40.) The nerves of the thymus arise from the par vagum or from the intercostal nerve. A milky humor is occasionally found in it in new-born infants. It has no known excretory duct, and hence its use is yet uncertain. Perhaps it secretes a lymph, which it pours through the lymphatics into the thoracic duct, for the dilution of the blood and the chyle, operating in this respect like the mesenteric glands and the pancreas. Hence its use is greater in the foetal state then after birth; because the foetus does not perform respiration, which is the grand agent in attenuating the blood, F. Bellinger is of opinion, that in the womb it prepares a liquid for the nutrition of the foetus, and sends this liquid to its mouth by particular ducts; but no one has hitherto been able to find any ducts of the kind." (Ibid., n. 256.)