Breast bone

Japanese: breast bone（英語表記）breastbone

...the lower opening of the thoracic cage is made up of the 12th thoracic vertebra, the lower end of the sternum (xiphoid process), and the left and right costal arches that stretch between them, and is naturally separated from the abdominal cavity by the diaphragm.
[sternum (breast bone)]
The sternum is a long, thin, flat bone located in the center of the front of the chest. It can be easily felt through the skin, and the bone marrow of this bone shows hematopoietic activity until old age, so it is used for bone marrow aspiration (sternal puncture), in which a needle is inserted to extract and test bone marrow. The sternum consists of three parts: the upper shaft, the middle body, and the lower xiphoid process.

From [Skeletal]

…Together with the clavicle, it connects the upper limbs to the trunk. Scapula, sternum, and ribs make up the thorax. It is located in the center of the front of the chest and has a long, flat shape. …

*Some of the terminology that mentions "breast bone" is listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

Japanese:

…胸郭の下口は第12胸椎，胸骨下端(剣状突起)，その間に張る左右の肋骨弓からなり，自然体では横隔膜によって腹腔と境されている。
［胸骨sternum(breast bone)］
　胸骨は胸の前面正中部にある一つの細長い扁平な骨で，皮膚を通して容易に触れることができ，しかもこの骨の骨髄は高齢まで造血活動を示すので，針をさして骨髄を採取し検査する骨髄穿刺（せんし）(胸骨穿刺)に用いられる。胸骨は上部の柄，中部の体，下端の剣状突起の3部からなる。…