小鼠淋巴结分布示意图

2. Superficial and deep lymph nodes Anatomical outline. In normal conditions, the lymph nodes of the mouse are easily detectable. They are numerous, of variable size in different strains of animals, greyish, and shaped as a small pea or bean. According to the localization, they can be classified as superficial lymph nodes, situated in the subcutaneous area and near the skeletal muscular masses, and as deep lymph nodes, situated inside the thoracic and abdominal cavity or close to the organs. Figure 5 shows a general picture of the morphological characteristics of every lymph node and its localization in the normal mouse. Fig. 5 Scheme reporting localization of the lymphatic system (from T. B. Dunn, 1954, courtesy of the Author) (Click on the image for a larger version) All superficial lymph nodes are bilateral and can be classified as: cervical superficial lymph nodes, situated immediately above the submandibular salivary glands; axillary lymph nodes, present in the axillary fossa; brachial and retroscapular lymph nodes, in proximity to the angle of the scapula; inguinal lymph nodes situated closed to the bifurcation of the superficial epigastric vein. The main deep lymph nodes are: the deep cervical lymph nodes, often difficult to localize, the more superficial ones are found in the cervical plane, hidden in the connective tissue that encircles the trachea; mediastinum or thoracic lymph nodes situated on the posterior face of the two lobes of the intimately connected thymus; the pyloric or pancreatic lymph nodes near the margin of the pancreas; the renal lymph nodes situated between the median margin of kidneys, more often at level of the hilum and in correspondence of the abdominal aorta; the mesenteric lymph node, of lengthened shape, that lies between the mesentery membranes, close to the ascending portion of the colon; the lumbar and caudal lymph nodes localized in proximity to the bifurcation of the aorta. Examination. Of the several lymph nodes, we will describe the particular characteristics as the shape, the volume, the consistency and the eventual relationships between them and the underlying plans. The lymph nodes near the centre of an inflammatory process frequently show increase of volume and sometimes haemorrhagic characteristics. Fig. 6 Observation of the mesenteric lymph node When, on the contrary, the whole lymphatic system of the animal is affected, this can be ascribed to a lymphoma. But also in these cases, the only character that can be observed macroscopically is enlargement which frequently is also of remarkable degree. Therefore, it will be more prudent to make a diagnosis of lymphoma, even if at this stage enough indicative, only when the necropsy is finished; alterations of the deep lymph nodes and of other organs, like the thymus, spleen and the liver, can be of help. The investigator must also examine, with particular attention, the state of the mesenteric lymph node. This lymph node in the mouse is found intimately connected, by means of mesentery, to the ascending colon (Fig. 6), and is easily detectable when the small intestine is reflected on the left side. In some diseases, the mesenteric lymph node can show remarkable variations in colour, consistency, and volume until becoming various times larger than the normal. This happens both in the lymphomas that in the mouse it is believed to originate just from the mesenteric lymph node, and in the so-called mesenteric syndrome described by Dunn (1954), in which you observe a marked proliferation of endothelial tissue, which forms numerous vessels overfilled by blood.