3. deep inguinal
4. internal iliac
5. external iliac
10. anterior sternal
If body tissues are invaded by disease-forming bacteria, some of the bacteria drift into the lymphatic system. The lymphatic system is arranged like a system of rivers leading to an estuary. The final opening of the system is called the right thoracic duct, and this returns the lymph to the vascular system at a point where the main veins of the body enter the heart. Lymph nodes with a gland-like appearance are located at regular intervals throughout the lymphatic system (Figure 1-27). Their function is to filter and destroy invading bacteria. When lymph nodes are successful, they prevent the spread of disease from the region of tissue that has been invaded. The activated lymphocytes of the lymphatic system may play a major role in attacking and destroying invading bacteria.
The lymph nodes that guard healthy tissues are compact in structure and pale brown in color.They become swollen and discolored when they are activated by invading bacteria. The meat inspector systematically examines the lymph nodes of the viscera and the dressed carcass. Lymph nodes that appear to be abnormal are sliced open for inspection. Knives must be re-sterilized once they have been used to open an infected lymph node. Once alerted to the presence of diseased tissue, the inspector determines the type and severity of the disease. The whole of the carcass or just the diseased parts may be condemned. It is essential, therefore, that any offals that have already been removed from the carcass can all be traced back to the carcass from which they originated. This also includes any blood which may have been collected as an ingredient for processed meat products. Blood for human consumption is usually collected with a hollow knife in order to minimize contamination from the surface of the carcass.