The thymus is relatively small, and is situated almost entirely in the
thorax. The left lobe is much larger than the right, and extends back as
far as the sixth rib at the time of its greatest size. According to Baum
the gland increases in size during the first two weeks after birth, and
atrophies rapidly in the next two or three months. Traces of it are
present at two or three years of age, and may be found even in old
subjects.