1. DEVELOPMENT OF
AXIAL SKELETON
Dr. Ahmed Fathalla Ibrahim

2. VERTEBRAL COLUMN

3. VERTEBRAL COLUMN
Mesenchymal cells from sclerotome are found in 3 areas:
Around notochord
Around neural tube
In body wall near to notochord & neural tube

4. VERTEBRAL COLUMN
Mesenchymal cells around notochord: form bodies of vertebrae
Mesenchymal cells around neural tube: form vertebral (neural) arches
Mesenchymal cells in body wall: form costal processes (give ribs in thoracic region)

5. FORMATION OF BODY At 4th week, each sclerotome is formed of:
A cranial part of loosely arranged cells
A caudal part of densely packed cells
The densely packed cells of one sclerotome fuse with the loosely arranged cells of succeeding sclerotome to form centrum (primordium of body)

6. FORMATION OF BODY As a result:
Each centrum develops from 2 adjacent sclerotomes (intersegmental)
Nerves lie in close relation to discs
Arteries (first intersegmental) now lie on each side of vertebral bodies
Notochord degenerates where it is surrounded by vertebral bodies

7. INTERVERTEBRAL DISC
Nucleus pulposus: notochord (between vertebral bodies)
Annulus fibrosus: surrounding mesenchyme

8. VERTEBRAL DEVELOPMENT

9. VERTEBRAL DEVELOPMENT Cartilaginous stage
At 6th week, chondrification centers appear
At the end of embryonic period, the 2 centers in centrum fuse then fuse with those of vertebral arches

10. VERTEBRAL DEVELOPMENT Bony stage
Primary ossific centers:
Present by the end of embryonic period
Three in number (one in centrum , one in each half of vertebral arch)
The 2 halves of vertebral arches fuse at 3-5 years (first in lumbar, fusion proceeds cranially)
Vertebral arches articulate with centrum through neurocentral joints until 3-6 years when fusion occurs

11. VERTEBRAL DEVELOPMENT Bony stage
Secondary ossific centers:
Appear after puberty
Five in number (two in body , one at tip of spinous process, one at tip of each transverse process)
All centers unite around 25 years

12. DEVELOPMENT OF RIBS
Ribs develop from costal processes in thoracic region:
They become cartilage during embryonic period
They ossify during fetal period
Site of union with vertebra is replaced by costovertebral joint
Costal processes in other region fuse with transverse processes of vertebrae

13. DEVELOPMENT OF STERNUM
Appears in the form of 2 vertical mesenchymal bars (sternal bars)
Fusion of 2 bars occurs craniocaudally
Chondrification occurs during fusion
Ossification centers appear craniocaudally before birth EXCEPT for xiphoid process (during childhood)

14. DEVELOPMENT OF CRANIUM
THE CRANIUM CONSISTS OF:
NEUROCRANIUM: PROTECTIVE CASE FOR BRAIN
VISCEROCRANIUM: SKELETON OF FACE
EACH PART IS SUBDIVIDED INTO:
CARTILAGINOUS PART: OSSIFY BY ENDOCHONDRAL OSSIFICATION
MEMBRANOUS PART: OSSIFY BY INTRAMEMBRANOUS OSSIFICATION

15. DEVELOPMENT OF CRANIUM

16. CARTILAGINOUS NEUROCRANIUM
PARACHORDAL CARTILAGE:
Forms around cranial end of notochord
Forms occipital bone (together with sclerotome of occipital somites)
HYPOPHYSEAL CARTILAGES:
Form around pituitary gland
Fuse to form body of sphenoid bone

17. CARTILAGINOUS NEUROCRANIUM
ALA ORBITALIS:
Forms lesser wing of sphenoid bone
OTIC CAPSULES:
Form petrous & mastoid parts of temporal bones
TRABECULAE CRANII & NASAL CAPSULES:
Fuse to form ethmoid bone

19. MEMBRANOUS NEUROCRANIUM
Forms the calvaria (cranial vault): frontal & parietal bones
Bones are separated by fibrous joints (sutures)
Six fontanelles (site of meeting of several sutures) are present

20. CARTILAGINOUS VISCEROCRANIUM
Derived from pharyngeal arches:
Dorsal end of 1st arch: malleus & incus
Dorsal end of 2nd arch: stapes & styloid process of temporal bone
Ventral end of 2nd arch: lesser horn & superior part of body of hyoid bone
Ventral end of 3rd arch: greater horn & inferior part of body of hyoid bone

21. MEMBRANOUS VISCEROCRANIUM
Squamous part of temporal bone
Maxillary bone
Zygomatic bone
Mandible

22. POSTNATAL GROWTH OF CRANIUM
At birth, calvaria is larger than face
Increase in size of calvaria is greatest during first 2 years (period of most rapid postnatal growth of brain)
Rapid growth of face & jaws coincide with:
Eruption of teeth
Development & enlargement of paranasal sinuses (which are absent or rudimentary at birth)

23. SPINA BIFIDA
Cause: Failure of fusion of the halves of the vertebral arch
Incidence: 0.04 – 0.15%
Sex: more frequent in females
Types:
Spina bifida occulta (20%)
Spina bifida cystica (80%)

24. SPINA BIFIDA

25. SPINA BIFIDA OCCULTA The closed type Only one vertebra is affected
No clinical symptoms
Skin over it is intact
Sometimes covered by a tuft of hair

26. with meningomyelocele
SPINA BIFIDA CYSTICA
with meningomyelocele
with myeloschisis

27. SPINA BIFIDA CYSTICA The open type Neurological symptoms are present
Subdivided into:
Spina bifida with meningocele: protrusion of sac containing meninges & cerebrospinal fluid
Spina bifida with meningomyelocele: protrusion of sac containing meninges with spinal cord and/or nerve roots
Spina bifida with myeloschisis: spinal cord is open (due to failure of fusion of neural folds)

28. CRANIOSYNOSTOSIS

29. CRANIOSYNOSTOSIS
Premature closure of cranial sutures (more severe if occurs prenatally)
Sex: more frequent in males
Types: depend upon which suture closes prematurely
Scaphocephaly (50%): sagittal suture
Oxycephaly (30%): coronal suture
Plagiocephaly: both coronal and lambdoid sutures on one side
Trigonocephaly: frontal suture