Anatomic location and age-related changes in the chinchilla thymus

Thymuses of chinchillas varying from 2 weeks to 8 years of age were studied grossly and histologically and were determined to be entirely intrathoracic. Histologically, the amount of actual thymic tissue in the older chinchillas appeared to be less than that in the younger chinchillas. Lymphocyte concentration within medullary centers of the older chinchillas was significantly (P less than 0.05) less than that of the younger animals. Lymphocytopoietic activity was evident in the oldest animals studied. Body weight and thymic mass (thymus plus adipose tissue) weight were greater (P less than 0.05) in the older chinchillas.