Medicine
Our knowledge of the lymphatic system has been very greatly increased during the past ten years by studies on its mode of development. Previous to 1902 nothing definite was known about the primary development or the mode of growth of the lymphatic system. It was concluded by some (Budge, Gullard and Saxer) that the lymphatics arise from undifferentiated mesenchyme cells; Ranvier believed that they arise from veins by budding of the endothelium; while Sala described them as arising partly from the mesenchyme and partly from venous endothelium.
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The spleen is a large blood-vascular organ closely associated with the lymphatic system.
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The lymph which enters the lymphatic capillaries passes over into collecting vessels (ducts), which carry it through the lymph-glands (nodes) to the large veins at the base of the neck. The lymph-vessels course in the loose subcutaneous tissues, in the connective tissues between muscles and organs, often accompanying the arteries and veins, sometimes forming networks around them. An idea of their arrangement can be best obtained by glancing at the illustrations of the lymphatics of special regions.
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The lymphatic capillary, like the blood-capillary, is the portion of the lymphatic system which is chiefly concerned in the specific function of this system. In the blood-capillaries, where the blood is separated from the outside tissues by a single layer of flat endothelial cells, there occurs the interchange of fluid substances and of cells, while the heart, arteries and veins serve to transport the blood, modified in the capillaries, to other parts of the body. Similarly in the lymphatic system, it is in the capillaries, both those most peripheral and those in the lymph nodes, where the absorption and interchange of fluid substances and of cells takes place. Consequently it becomes of prime importance to obtain a clear understanding of the structure of the lymphatic capillaries, their relation to the other tissues, and their mode of functioning. At the outset, however, it must be admitted that our knowledge on this subject is far from complete.
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The heart is a hollow muscular organ, divided by a longitudinal septum into a right and a left half, each of which is again subdivided by a transverse constriction into two compartments, communicating with each other, and named auricle and ventricle. Its general form is that of a blunt cone. Enclosed, as before said, in the pericardium, it is placed behind the sternum and the costal cartilages, the broader end, or base being directed upwards, backwards, and to the right, and extending from the level of the fifth to that of the eighth dorsal vertebra ; the apex downwards, forwards, and to the left.
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The thyroid gland has only topographic relations to the organs of the respiratory tract; in other respects it belongs to the ductless glands (glands with internal secretions). It is situated in the neck in front of the trachea and the lateral portions of the larynx, and is also partly in contact with the lateral wall of the laryngopharynx. Its middle portion is covered by the superficial layer of the deep cervical fascia, and laterally it is immediately beneath the sternothyreoidei, which lie upon the gland, the remaining infrahyoid muscles, the inner margin of the sternocleidomastoideus, and the platysma.
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The vagina (French: le vagin) is a rather capacious and markedly dilatable musculo-mucous canal, which extends from the uterus to the external genitalia. When collapsed it is markedly flattened from before backward, so that its lumen corresponds to the letter H, the anterior and posterior walls being in contact, while small recesses occur on either side. The anterior wall is usually concave posteriorly, the posterior wall being correspondingly convex anteriorly.
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The pancreas (French : pancréas) is a long, narrow, flattened gland of a reddish cream color, larger at one end than at the other, and lying across the posterior wall of the abdomen, behind the stomach, and opposite the first lumbar vertebra. Its larger end, the head, turned to the right, is embraced by the curvature of the duodenum, whilst its left or narrow extremity, the tail, reaches to a somewhat higher level, and is in contact with the spleen. The pancreas is an exocrine and endocrine gland. It is in contact with the lumbar column, therefore particularly exposed with the abdominal traumatisms.
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The trachea is a rather rigid and constantly open tube, 10 to 12 cm- long and 11 to 18 mm. wide, which leaves the larynx at the level of the intervertebral disc between the sixth and seventh cervical vertebrae and extends to that of the disc between the fourth and fifth thoracic vertebrae. In the latter situation or in front of the fifth thoracic vertebra it divides into two branches, the bronchi, which form a right angle with each other. This division is called the tracheal bifurcation.
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The liver is the largest gland of the human body.It has the shape of a flattened ellipsoid, passes almost transversely across the upper portion of the abdominal cavity, and is composed of two lobes, a much larger right lobe and a smaller left one. It is soft in consistence and has a peculiar brownish-red color.
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The large intestine is an approximately cylindrical tube from 120 to 150 cm. in length and of variable width. It is composed of two main portions: the ccecum, with the vermiform appendix, and the colon. These two portions, exactly alike and not sharply demarcated, are arranged in a large horseshoe loop about the small intestine, the large intestine becoming continuous with the rectum on the left.
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