OSSIFICATION OF THE VEETEBE^E. 



105 



nucleus (Quain). The transverse processes are completed by epiphyses about the eight- 

 eenth year (Fawcett). The, anterior arch is developed from centres variously described 

 as single or double, which appear in the hypochordal arch of cartilage described by 

 Froriep (Arch. f. Anat. u. Physiol., Anat. Abth. 1886) which here persists. In this 

 cartilage ossification commences during the first year of life. Union with the lateral 

 masses is delayed till six or eight years after birth. The lateral extremities of the 

 anterior arch assist in forming the anterior part of the superior articular processes. 



Epistropheus. The epistropheus ossifies from five primitive centres. Of these, two 

 one on each side appear about the seventh week, and form the articular and transverse 

 processes, together with the laminae and spinous process. One, or it may be two, nuclei 

 appear in the inferior part of the body about the fifth month. The superior part of the 

 body, including a small part of the superior articular process, and the base of the dens, 



19 



Cervical vertebra. 



1. Centre for body. 



2. Superior epiphysial plate. 



3. Anterior bar of transverse process developed by 



lateral extension from root of vertebral arch. 



4. Neuro-central synchondrosis. 



5. Inferior epiphysial plate. 



Lumbar vertebra. 



6. Body. 



7. Superior epiphysial plate. 



8. Epiphysis for mamillary process. 



9. Epiphysis for transverse process. 



10. Epiphysis for spinous process. 



11. Neuro-central synchondrosis. 



12. Inferior epiphysial plate. 



Tlwracic vertebra. 



13. Centre for body. 



14. Superior epiphysial plate, appears about puberty ; 



unites at 25th year. 



15. .Neuro-central synchondrosis does not ossify till 



5th or 6th year. 



16. Appears at puberty ; unites at 25th year. 



17. Appears at puberty ; unites at 25th year. 



18. Appears about 6th week. 



Epistropheus. 



19. Centre for transverse process and vertebral arch ; 



appears about 8th week. 



20. Synchondroses close about 3rd year. 



27 SI 



FIG. 119. OSSIFICATION OF VERTEBRA. 



21. Centre for summit of dens ; appears 3rd to 5th 



year, fuses 8th to 12th year. 



22. Appears about 5th or 6th month ; unites with 



opposite side 7th to 8th month. 



23. Synchondrosis closes from 4th to 6th year. 



24. Inferior epiphysial plate ; appears about puberty, 



iinites about 25th year. 



25. Single or double centre for body ; appears about 



5th month. 



Atlas. 



26. Posterior arch and lateral masses developed from 



a single centre on either side, which appears 

 about 7th week. In this figure the posterior 

 arch is represented complete by the union 

 posteriorly of its posterior elements. 



27. Anterior arch and portion of superior articular 



surface developed from single or double centre, 

 appearing during 1st year. 



Thoracic vertebra. 



28. Epiphysis for transverse process ; appears about 



puberty, unites about 25th year. 



29. Epiphysis appears about puberty ; unites about 



25th or 27th year. 



30. Centre for vertebral arch on either side ; appears 



about 6th or 7th week, the laminae unite from 

 birth to 15th month. The arch is here shown 

 complete posteriorly. 



31. Centre for body ; appears about 6th week, unites 



with vertebral arch from 5th to 6th year. 



are developed from two laterally-placed nuclei which appear shortly after, and fuse together 

 at the seventh or eighth month, so that at birth the bone consists of four pieces. Fusion 

 between these parts takes' place in the following order : The dens unites with the body 

 and lateral parts about the third or fourth year ; union between the two lateral portions 

 posteriorly and- the body and lateral parts anteriorly, is complete at from four to six years. 

 The summit of the dens is developed from a separate centre, occasionally double, 

 which appears from the third to the fifth year, and fuses with the rest of the bone from 

 the eighth to the twelfth year. About puberty an annular epiphysis is developed on the 

 inferior surface of the body, with which it is completely united during the twentieth to 

 the twenty-fifth year. Some authorities state that a few granules between the base of the 

 dens and the superior surface of the body represent the superior epiphysial plate ; but 



