Embryology

Question 1

First branchial arch (mandibular)

Answer 1

(1) Nerve: trigeminal (V)
(2) Muscle: muscles of mastication, tensor veli palatini, mylohyoid, anterior digastrics, tensor tympani
(3) Skeletal structure: sphenomandibular ligament, anterior malleal ligament, mandible, malleus, incus
(4) Artery: maxillary
(5) Pouch and derivative: eustachian tube, middle ear
* Hillocks of His 1-3: tragus, helical crus, helix

Question 2

Second branchial arch (hyoid)

Answer 2

(1) Nerve: facial (VII)
(2) Muscle: stapedius, posterior digastrics, stylohyoid, muscles of facial expression
(3) Skeletal structure: stapes, styloid process, stylohyoid ligament, lesser cornu/upper portion of hyoid
(4) Artery: stapedial
(5) Pouch and derivative: palatine tonsil
* Hillocks of His 4-6: antihelix, antitragus, and lobule

Question 3

Third branchial arch

Answer 3

(1) Nerve: glossopharyngeal (IX)
(2) Muscle: stylopharyngeus
(3) Skeletal structure: greater cornu of the hyoid, lower body of hyoid
(4) Artery: common and internal carotid
(5) Pouch and derivative: thymus and inferior parathyroid

Question 4

Fourth branchial arch

Answer 4

(1) Nerve: superior laryngeal (X)
(2) Muscle: constrictors of the pharynx, cricothyroid
(3) Skeletal structure: laryngeal cartilages
(4) Artery: subclavian on right, arch of aorta on left
(5) Pouch and derivative: superior parathyroid, parafollicular cells of thyroid

Question 5

Sixth branchial arch

Answer 5

(1) Nerve: recurrent laryngeal (X)
(2) Muscle: intrinsic laryngeal muscles
(3) Skeletal structure: laryngeal cartilages
(4) Artery: pulmonary artery on right, ductus arteriosus on left

Question 6

Embryologic pathophysiology of gliomas, meningoceles, or encephaloceles vs dermal sinuses or dermoids

Answer 6

Persistent dural-dermal connection via foramen cecum and pre-nasal space (or less frequently via fonticulus frontalis) = above vs below