Fill in the Blanks Bones embro developmentOnline version A&P unit 2/laboptom by Kirsten Storemski 1 mesenchymal ossification skull compact membrane bone Intramembranous fontanels mandible Ossification Osteoblasts mesenchyme periosteum Trabeculae Endochondral ossification and intramembranous ossification are both ways that fetal bones are developed . Both types of bones are remodeled later . After remodeling , cannot tell which type is which . starts with formation of membrane . Ossification begins at 8 weeks of gestation , and is completed by two years . Some examples are the and bones . The steps are the formation of which is collagen fibers and cells . These cells differentiate into osteoblasts that surround fibers and make the matrix . is made and more layers are laid on the trabeculae . They interconnect to form cancellous bone . Spaces between for red bone marrow . Cells on perimeter of bone differentiate to form . under periosteum lay down . begins in ossification centers . Membrane spaces between ossification centers are called .
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