Electron microscopy of the thymus in two species of snakes, Crotalus atrox and Lampropeltis getulus

The lymphoid cell population of thymus in the rattlesnake and king snake is similar to that of mammals. Lymphocytes occupy the interstices of an epithelial cell framework. An abudance of tonofilaments and desmosomes occupy the cytoplasm of epithelial cells with light, homogeneous nuclei and prominent nucleoli. Other epithelial cells contain phagocytized material in a dense cytoplasm which surrounds an irregular nucleus with heavily clumped chromatin. Small, granular vesicles are found within some epithelial cells. Myoid cells occur in the medullary area. In mature forms, myofibrils are arranged in a concentric fashion around the nucleus and occupy much of the cytoplasmic volume. The presence of developmental stages of these cells suggests their differentiation within the thymus of the adult animal.