DEVELOPMENT OF THE HEAD AND NECK - 1

• Cartilaginous Neurocranium (Chondocranium): Neurocranium that develops by endochondral ossification (with a cartilaginous intermediate)
• Membranous Neurocranium: That part of the skull that develops by membranous ossification.
• The Frontal and Parietal bones are membranous.
• Sutures are connections between bones. They allow for growth of the cranium.
• Fontanelles occur at the intersection of two sutures.
• There are six of them.
• The Anterior Fontanelle stays open until the middle of the 2nd year.
• Craniostenosis is the failure for the skull to expand due to malformed sutures.

Viscerocranium: The rest of the skull, not overlying the brain. The Maxilla, Mandible, and facial skeleton.

• Endochondral Viscerocranium:
• The middle ear bones are endochondral.
• Styloid Process of Temporalis
• Greater Cornu and Inferior body of the Hyoid
• Laryngeal Cartilages
• Membranous Viscerocranium: Maxillary and Mandibular Prominences

Special Visceral Efferent (SVE) Fibers:

• They all innervate Branchial Muscles, derived from Branchial arches
• They all originate from the Nucleus Ambiguus.

General Visceral Efferent (GSE, GVE) Fibers:

o They innervate muscles that are derived from somites.

Branchial (Pharyngeal) Arches: They are primitive gills in the neck region of the embryo.

o In humans, we form a primitive gill but then we don't break down the membranes to form mature gills.

o This is an example of ontogeny recapitulating phylogeny, and so is the Mesonephric Duct of the Kidney, which develops and then disintegrates, being replaced by metanephric duct.

o Two different types of mesenchyme compose the Neural Arches:

§ Neural Crest: Forms the Arch Cartilages. The arch cartilages are made of neural crest! So this would be ectodermal (neural crest) mesenchyme.

§ Mesodermal: The rest of the neural arch is mesodermal mesenchyme.

Branchial Pouches: The outpocketing of endoderm, or the endodermal component on the inside of each arch.

Branchial Clefts (Grooves): The ectodermal ingrowths, found in between each set of arches.

Category: Anatomy Notes