Anatomy

 

 

 

The splenic artery, [a. splenica, ], in the adult the largest branch of the coeliac artery, is destined to supply the spleen, and in part the stomach and pancreas. It is directed horizontally towards the left side.

The pulmonary veins return the aerated blood from the lungs to the heart.

The hepatic artery, [a. hepatica, french : artère hépatique], which is intermediate in size, at least in the adult, between the coronary and splenic arteries, gives branches to the stomach, the duodenum, and the pancreas, besides supplying the liver and gall-bladder.

Closely associated with the lymphatic capillaries and vessels is a group of glandular structures known as lymphoid organs. They consist, essentially, of groups of round lymphoid cells, lying in a meshwork of reticulum fibers, and having often a definite relationship to the blood or lymph vessels.

The coronary artery of the stomach (coronaria ventriculi ; French : coronaire stomachique), the smallest of the three visceral branches derived from the coeliac artery, inclines upwards, and to the left side, to reach the cardiac orifice of the stomach.

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.

The coeliac artery, [a. coeliaca, French : tronc cœliaque] , a short and very thick vessel, arises from the aorta close to the margin of the diaphragm. In the erect position of the body its direction is nearly horizontal forwards, and it is not more than half an inch long.

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.

­­­The deep­ veins, although posterior in their appearance with the surface veins acquired in the adult, by the development of the muscular masses, a volume usually higher than that of the subcutaneous veins.

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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.

The superior or descending vena cava carries to the heart the blood returned from the head and neck and upper extremities through the right and left innominate veins, and from the walls of the thorax, either directly through the greater azygos vein, or indirectly through the innominate veins.

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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