• Three Regions of the Skull
• (1) neurocranium (vault) – made up of membranous bones: frontal, parietal (2), temporal (2), occipital
• occipital and temporals also have cartilaginous growth centers Þ basilar part of occipital petrous, mastoid, tympanic parts of the temporal
• (2) viscerocranium (facial skeleton) – skull bones not bounding brain: nasal, maxillae, zygomatic, palatine, mandible
• may also be defined to include the frontal bone and the zygomatic processes of the temporals
• (3) chondrocranium (skull base) – growth via synchondroses between the sphenoid and the ethmoid, temporals, and occipital
• three fossae in the base: anterior, middle, posterior; anterior/middle separated by the clinoid crests of the lesser wing of the sphenoid, middle/posterior separated by the petrous apices
• Sutures:
• metopic – divides the frontal bone in infants; suture is usually invisible by age 6
• coronal – between the frontal and parietal bones
• lambdoid – between the parietal and occipital bones
• saggital – between the two parietal bones
• Fontanelles:
• anterior: at junction of frontal and parietal bones; closes by 18^th month; becomes the adult bregma (intersection of sagittal and coronal sutures)
• posterior: at junction of occipital and parietal bones; closes by 6^th month; becomes the adult lambda (intersection of sagittal and lambdoid sutures)
• sphenoidal (antero-lateral): becomes adult pterion (junction of frontal, parietal, temporal, sphenoid bones)
• mastoid (postero-lateral): becomes adult junction of parietal, occipital, temporal bones

• I - XII : olfactory, optic, oculomotor, trochlear, trigeminal, abducent, facial, vestibulocochlear (auditory), glossopharyngeal, vagus, accessory, hypoglossal
• Mnemonics:
• the names: Oh Oh Oh To Touch And Feel A Girl’s Vagina – Ah Heaven!
• sensory, motor or both: Some Say Marylin Monroe, But My Brother Says Bridgette Bordoe Mad Man
• Special sensory nerves: olfactory, optic, vestibulocochlear (auditory)

Branchial Arches – "branchial" is derived from the Latin for "gill"

• 4 pairs of arches visible by the 4^th week; the 5^th arch is often rudimentary or absent; the 6^th arch is not externally visible
• arches are lined by endoderm of the pharynx on the inside, ectoderm on the outside, and intervening mesenchyme containing an aortic arch, a cranial nerve, and a cartilaginous rod
• mesenchyme of the arches is derived from migrating neural crest cells which differentiate into mesenchyme (distinct from the mesenchyme in the rest of the embryo)
• branchial grooves separate the arches and are made up of the ectoderm between the arches
• branchial pouches are analogous to the grooves but on the inside of the pharynx; made up of endoderm
• branchial membranes: areas between the arches where the ectoderm of the groove and the endoderm of the pouch are adherent to each other without any mesenchyme separating them
• Derivatives of Branchial Structures:
• 1^st Branchial Arch
• nerve: Cranial Nerve V (trigeminal)
• arch: maxillary prominanceÞ maxilla, zygomatic, and part of temporal bone; mandibular prominanceÞ mandible
• cartilage: Meckel’s cartilage, gives rise to mandible, maleus and incus of ear
• pouch: tympanic membrane and cavity; also eustachian tube (maintains communication of middle ear with pharynx)
• groove: external auditory meatus
• membrane: tympanic membrane (1^st membrane is the only one that contributes to an adult structure)
• 2^nd Branchial Arch
• nerve: Cranial Nerve VII (facial)
• arch: hyoid arch, gives rise to superior portion of the hyoid bone
• cartilage: Reichert’s cartilage, gives rise to stapes of ear, styloid process of temporal bone
• pouch: palatine tonsil
• 3^rd Branchial Arch
• nerve: Cranial Nerve IX (glossopharyngeal)
• cartilage: inferior part of hyoid bone
• pouch: inferior parathyroid gland, thymus
• 4^th and 6^th Branchial Arches
• nerve: Cranial Nerve X (vagus)
• cartilage: laryngeal cartilage
• pouch (considered to be the fusion of the 4^th and 6^th pouches): superior parathyroid gland; thyroid C cells

• Thyroid – forms from laryngeal endoderm and migrates down the thyroglossal duct ventral to the pharyngeal cartilage
• foramen cecum of tongue is the remnant of the proximal end of the duct
• pyramidal lobe of the thyroid is the distal end of the duct (only found in some people)
• Tongue – anterior 2/3 (anterior to foramen cecum) Þ derived from 1^st arch so receives trigeminal (CN V) innervation
• posterior 1/3 Þ derived from the 3^rd arch so receives glossopharyngeal (CN IX) innervation