Development of the Skull The skull consists of a neurocranium that forms a protective case, which surrounds the brain and special sensory organs (optic, auditory, and olfactory), and a viscerocranium (facial skeleton, or splanchnocranium) that forms the ear ossicles, hyoid bone, laryngeal and tracheal cartilages, and certain processes of the skull.

1.Neurocranium: Neural crest cells surround the neural tube form the sclerotome ; the origin of both cartilage and bones. 2.Cartilaginous Neurocranium (Chondrocranium): Consists of a basal plate, trabecular region, and cartilaginous sensory capsules that surround the organs of special sense (acoustic and vestibular, olfactory, and possibly optic). 3.Membranous Neurocranium (Dermatocranium):Form the large flat bones that cover the brain and facial region, including the frontals, parietals, part of the occipital, and the squamous temporal bones. 4.Viscerocranium: Develops from the pharyngeal (branchial) arches that are apparent in the neck region during the fourth week of development. Types of Skull bones:

Modes of Ossification: 1.Membranous ossification. 2.Endochondral ossification.

Endochondral ossification The mesodermal Cells transform Into procartilage, then cartilage, Breakdown of Cartilage cells and Formation of Osteogenic tissue.