Thymus of the dog

The cortex stains darker than the medulla because the former is mostly made up of densely packed lymphocytes. The cortex also appears to have little holes in the tissue. This ‘mooth-eaten” appearance is due to the presence of macrophages sitting in a clear area among the tightly packed lymphocytes. Notice the blood vessels at thr junctions between the cortex and the medulla. PK2966-97. H&E Thymus. Immune system. Dog.