The thoracic inlet is bounded by : the first thoracic vertebra ( T1 ) " posteriorly ", the first pair of ribs " laterally " ( more specifically, the first ribs form lateral C-shaped curves posterior to anterior ), the costal cartilage of the first rib and the superior border of the manubrium " anteriorly ".
42.
The ossification centers appear in the intervals between the articular depressions for the costal cartilages, in the following order : in the manubrium and first piece of the body, during the sixth month of fetal life; in the second and third pieces of the body, during the seventh month of fetal life; in its fourth piece, during the first year after birth; and in the xiphoid process, between the fifth and eighteenth years.
