All of the following muscles are derived from second branchial arch except:
**Core Concept**
The branchial arches are a series of embryological structures that give rise to various muscles, bones, and nerves in the head and neck region. Each branchial arch is associated with a specific cranial nerve and develops into distinct muscles and structures. Understanding the embryological origins of muscles is crucial for identifying their innervation and function.
**Why the Correct Answer is Right**
The muscles derived from the second branchial arch are primarily innervated by the facial nerve (cranial nerve VII), which supplies the muscles of facial expression, including the buccinator, orbicularis oculi, and orbicularis oris. The second branchial arch muscles are also involved in the formation of the stapedius and the stylohyoid muscles. The correct answer will be a muscle not innervated by the facial nerve or derived from the second branchial arch.
**Why Each Wrong Option is Incorrect**
* **Option A:** The digastric muscle is primarily derived from the first and second branchial arches, with the anterior belly innervated by the mandibular division of the trigeminal nerve (cranial nerve V3) and the posterior belly innervated by the facial nerve (cranial nerve VII). However, since it is partially derived from the second branchial arch, it might initially seem like a plausible choice.
* **Option B:** The stylohyoid muscle is derived from the second branchial arch and is innervated by the facial nerve (cranial nerve VII). Therefore, it is not the correct answer.
* **Option C:** The tensor tympani muscle is derived from the first branchial arch and is innervated by the mandibular division of the trigeminal nerve (cranial nerve V3). This muscle is not derived from the second branchial arch and is therefore the correct answer.
**Clinical Pearl / High-Yield Fact**
It is essential to remember that the muscles of facial expression, including the buccinator, orbicularis oculi, and orbicularis oris, are all derived from the second branchial arch and are innervated by the facial nerve (cranial nerve VII). This knowledge is crucial for identifying the correct muscles and their innervation patterns in clinical practice.
**Correct Answer:** C. Tensor tympani muscle.