The third week of development is characterized by the appearance of the branchial apparatus, the embryonic primordium from which head and neck structures will be derived. The apparatus consists of five branchial arches, numbered 1, 2, 3, 4 and 6. Second arch anomalies represent 95% of all branchial anomalies and are classified into four types with types IIII being the most common. The anomalies manifest as cysts or fistulae in the lateral neck, located anterior and deep to the sternocleidomastoid muscle. Which of the following structures develop from the second branchial arch?
- anterior digastric muscle
- posterior cricoarytenoideus muscle
- posterior digastric muscle
- stylopharyngeus muscle
- superior constrictor muscle
Answer(s): C
Explanation:
The posterior digastric muscle is derived from the second branchial arch and thus is innervated by its nerve, the facial (Seventh cranial) nerve. The anterior digastric muscle (choice A) is derived from the first branchial arch and is innervated by its nerve, the mandibular division of the trigeminal (fifth cranial) nerve.
The posterior cricoarytenoideus muscle (choice B) and the superior constrictor muscle (choice E), derived from a combination of the fourth and sixth branchial arches, are innervated by the vagus (tenth cranial) nerve. The stylopharyngeus (choice D) is derived from the third branchial arch and is the only voluntary muscle innervated by the glossopharyngeal (ninth cranial) nerve.