The thymus gland is situated in the upper part of the anterior mediastinum, extending up in front of the trachea nearly as high as the thyroid. It attains its largest size about the second year of life, remains stationary from that time till the fourteenth year, and then gradually atrophies. The atrophy is associated with an infiltration of adipose tissue. By some the gland is regarded as lymphatic in structure and function, but embryologically it seems to have an epithelial origin. It contains round bodies which are sometimes calcified, the so-called Concentric bodies of Hassall.

The thymus is liable to Inflammations like other glands. Hypertrophy also occurs, and cases of asthma and of spasm of the glottis resulting sometimes in sudden death have been ascribed to this condition, but without sufficient evidence.

Enlargements occur in Leukaemia and in Hodgkin's disease, the relation of the organ to the spleen and lymphatic glands being thus indicated.

Tumours also occur, chiefly sarcomas, and cancers.

Syphilis sometimes manifests itself by the presence of gummata. Tuberculosis, according to Jacobi, is not of infrequent occurrence, both as a local affection and in general tuberculosis.

Literature

Sanne, in Diet, encycl. des sc. med., Article Thymus, 1887; Jacoisi, Comptes rendus du Congres pour l'etude de la tuberculose, 1888, and Anat. and Path, of thymus, Trans. Assoc, of Amer. Phys., Sept., 1888.