The structure of the sternal bursa of turkeys.

The sternal bursa developed as a microscopically recognizable synovial sac in turkeys at about 4 1/2 to 6 weeks of age. In birds 12 weeks old it was difficult to delineate the bursa grossly although microscopically it was a definite structure. After 12 weeks, the walls of the bursa were thick enough that the limits of the sac could be determined grossly. The synovial membrane was in the subcutis, and microscopically was a vascular band of loose to dense connective tissue of variable thickness. Laterally the membrane was folded so that in cross section it appeared as a tonguelike projection of variable length into the cavity. The lining cells centrally were flat fibroblasts while laterally they were cuboidal, particularly over the lateral folds. In older turkeys the cuboidal lining cells were sometimes stratified.