71. Which labeled part is the smallest part of the sternum and is comprised of cartilage at birth but develops into bone in adulthood?
Answer: B
The xiphoid process is the smallest part of the sternum and is initially made of cartilage that ossifies into bone in adulthood.
The xiphoid process is the smallest segment of the sternum, beginning as cartilage during infancy and gradually ossifying into bone as a person matures.
A) Body
The body of the sternum is the largest part and serves as the central section that articulates with the ribs. It is not the smallest part and does not have the cartilage-to-bone development characteristic noted in the question.
B) Xiphoid process
The xiphoid process is indeed the smallest part of the sternum and is made of cartilage at birth, which later turns into bone in adulthood. This option correctly matches the description provided in the question.
C) Manubrium
The manubrium is the uppermost portion of the sternum and is larger than the xiphoid process. It does not fit the criteria of being the smallest part or undergoing the specified cartilage-to-bone transformation.
D) Sternal angle
The sternal angle is not a part of the sternum but rather a feature formed at the junction of the manubrium and the body of the sternum. It does not qualify as a part of the sternum and does not relate to the cartilage-to-bone development described.
Conclusion
The xiphoid process is definitively the correct answer as it accurately represents the smallest part of the sternum that starts as cartilage and develops into bone during adulthood. All other options either refer to larger components of the sternum or do not conform to the specific characteristics outlined in the question.