IMMUNE SYSTEM

The lymphatic vessels and lymph nodes are similar to those in most mammals. The mesenteric lymph node is the largest lymph node and is often embedded in fat in obese rats.

Thymus

Most of the thymus lies in the cranial mediastinum, with a small cervical part lying ventral to the trachea. Like all rodents it persists into adult life (Bivin et al. 1979; Percy & Barthold 2001).

Figure 10.9 • Lateral radiograph of rat skull.

Spleen

The spleen lies in the left dorsal cavity between two layers of omentum. It is oblong in shape and larger in males than in females. It is a major site of red cell breakdown (Bivin et al. 1979).