Sequence of ossification in human vertebral neural arch centers

The purpose of the present study is to determine whether ossification of the human vertebral neural arches follows a craniocaudal sequences of development or develops in separate groups from the lower cervical/upper thoracic, upper cervical, and lower thoracic/upper lumbar regions as described by Bagnall et al. (1977b) in a radiographic study. Seven formalin-fixed, two fresh frozen, and six serial-sectioned human embryos and fetuses, ranging in crown-rump length (C-R) from 27 mm to 76 mm, were examined. A procedure adapted by Watson (1977a,b) for in toto staining of whole specimens with alcian blue and alizarin red S for cartilage and bone was used, whereas serial sections were stained with hematoxylin and eosin, or Koneff's stain (1960). The intact specimens demonstrated a vivid deep blue cartilaginous skeleton with differentiated red areas of bone development seen through soft tissues rendered transparent by potassium hydroxide or enzyme clearing. The ossification sequence of the neural arches differed from the conventional craniocaudal descriptions given in anatomical textbooks. Neural arch ossification was found to commence in the lower cervical/upper thoracic regions, quickly followed by a second group in the lower cervical region, and subsequently a third group in the lower thoracic/upper lumbar region.