A 3-day-old neonate born to non-consanguineous parents presents with severe respiratory distress and cyanosis. Physical examination reveals a small mandible, cleft palate, and micrognathia. Chest X-ray shows bilateral lung hypoplasia. Genetic testing reveals a heterozygous deletion in chromosome 22q11.2 (DiGeorge syndrome). The neonatologist explains that the cleft palate and mandibular hypoplasia result from abnormal neural crest cell migration during weeks 5–7 of development. Which of the following structures is NOT derived from neural crest cells and therefore would NOT be expected to be affected in this condition?