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 smallest part of the sternum is the xiphoid process, which is cartilage at birth and develops into bone in adulthood.
The xiphoid process is the smallest part of the sternum, beginning as cartilage during infancy and ossifying into bone as a person matures. This characteristic makes it distinct among the various components of the sternum.
A) Body
The body of the sternum is the largest and central part, located between the manubrium and the xiphoid process. It does not serve as the smallest part and is primarily composed of bone throughout adulthood.
B) Xiphoid process
The xiphoid process is indeed the smallest part of the sternum, initially made of cartilage at birth. It is unique as it transitions to bone during adulthood, making it the correct choice in this context.
C) Manubrium
The manubrium is the uppermost portion of the sternum and is larger than the xiphoid process. It does not undergo the same transformation from cartilage to bone, which further distinguishes it from the correct answer.
D) Sternal angle
The sternal angle is not a part of the sternum itself, but rather a junction between the manubrium and the body of the sternum. It is not involved in the transformation from cartilage to bone, making it irrelevant to the question.
Conclusion
The xiphoid process is the smallest and only part of the sternum that starts as cartilage and later ossifies into bone. All other options either refer to larger components of the sternum or are not parts that undergo this specific developmental change, confirming that the xiphoid process is the definitive correct answer.