EMBRYONIC DEVELOPMENT & STEM CELL COMPENDIUM
EMBRYONIC DEVELOPMENT & STEM CELL COMPENDIUM
67. Appendicular Skeleton and Skull Development
Review of MEDICAL EMBRYOLOGY Book by BEN PANSKY, Ph.D, M.D.
- The appendicular skeleton consists of the shoulder (pectoral) and pelvic girdles as well as the bones of the limbs
- DURING WEEK 6, the mesenchymal primordia of bones in the limb buds undergo chondrification to form hyaline cartilage models of the future bones
- The clavicle initially develops by intramembranous ossification but does form growth cartilages at both ends
- The pectoral girdle and upper limb cartilages appear before those of the pelvic girdle and lower limbs. The cartilages appear in a proximodistal sequence
- OSSIFICATION in long bones begins by the end of the embryonic period; the primary centers are seen by week 12 in almost all bones of the extremities; and secondary ossification centers are seen after birth
- The skull develops from mesenchyme around the developing brain and consists of a neurocranium, which forms a protective case around the brain, and a viscerocranium, which forms the skeleton of the face
- THE NEUROCRANIUM consists of 2 parts: the cartilaginous base of the skull or chondrocranium and a membranous portion which forms the flat bones around the brain
- Size of the skull is large in proportion to the rest of the skeleton, and the face is small when compared to the cranium in the newborn. Postnatally, the cranial vault grows rapidly to 7 years as a result of brain growth. The face and jaws also develop rapidly with the development of the teeth and paranasal sinuses
