1. The Skull Its bones can be divided into : Its bones can be divided into : 1. NEUROCRANIUM 1. NEUROCRANIUM It forms a protective case around the brain. It forms a protective case around the brain. 2. VISCEROCRANIUM 2. VISCEROCRANIUM It forms the skeleton of the face. It forms the skeleton of the face.

2. NEUROCRANIUM Is divided into: Is divided into: (A) Membranous (A) Membranous It forms Flat bones of (Calvaria) or Cranial Vault, which surround the brain. It forms Flat bones of (Calvaria) or Cranial Vault, which surround the brain.

3. NEUROCRANIUM (B) Cartilaginous part (Chondrocranium) (B) Cartilaginous part (Chondrocranium) It forms the bones of the base of the skull. It forms the bones of the base of the skull.

4. MEMBRANOUS NEUROCRANIUM Mesenchymal cells derived mostly from the Neural Crest and partly from the Para Axial mesoderm. Mesenchymal cells derived mostly from the Neural Crest and partly from the Para Axial mesoderm. They ossify directly into bone: (flat bones) They ossify directly into bone: (flat bones) at the top and most of the sides of the brain. at the top and most of the sides of the brain.

5. SUTURES At birth, the neural crest cells form condensed Fibrous joints between the flat bones of the skull. At birth, the neural crest cells form condensed Fibrous joints between the flat bones of the skull.

6. FONTANELLS They are at the meeting of more than two sutures which becomes wide. They are at the meeting of more than two sutures which becomes wide. The fontanells are (6) in number. The fontanells are (6) in number. The Anterior Fontanell is the most prominent. The Anterior Fontanell is the most prominent. Its palpation gives an idea about the intracranial pressure and the process of ossification of the skull. Its palpation gives an idea about the intracranial pressure and the process of ossification of the skull.

7. MOLDING It is adaptation of the shape of the fetal skull to the pelvic cavity during birth. It is adaptation of the shape of the fetal skull to the pelvic cavity during birth. It depends on the softness of the bones and their loose connections at the sutures to allow the overlapping of the bones of the skull. It depends on the softness of the bones and their loose connections at the sutures to allow the overlapping of the bones of the skull.

8. MOLDING 1. The Frontal bone becomes flat. 1. The Frontal bone becomes flat. 2. The Occipital bone is drawn out. 2. The Occipital bone is drawn out. 3. Slight overriding of one Parietal bone on the other. 3. Slight overriding of one Parietal bone on the other. Restoration of the normal shape is within few days after birth. Restoration of the normal shape is within few days after birth.

9. CHONDROCRANIUM It is formed by fusion of several separate cartilages. It is formed by fusion of several separate cartilages.

10. (1) PARACHORDAL CARTILAGE (BASAL PLATE) It is the cartilage in around the rostral limit of the notochord. It is the cartilage in around the rostral limit of the notochord. It is derived from the paraxial mesoderm. It is derived from the paraxial mesoderm.

11. PARACHORDAL (BASAL) PLATE It fuses with the cartilages derived from the Sclerotomes of the occipital somites (somitomers). It fuses with the cartilages derived from the Sclerotomes of the occipital somites (somitomers).

12. PARACHORDAL PLATE It forms the Base of the Occipital bone. It forms the Base of the Occipital bone. It extends around the cranial end of the spinal cord to form the boundaries of the foramen magnum. It extends around the cranial end of the spinal cord to form the boundaries of the foramen magnum.

13. (2) HYPOPHYSEAL CARTILAGE It is formed around the developing pituitary gland,rostral to the occipital basal plate. It is formed around the developing pituitary gland,rostral to the occipital basal plate. It is derived from the Neural Crest cells. It is derived from the Neural Crest cells. Its cartilage fuses to form the Body of the sphenoid bone. Its cartilage fuses to form the Body of the sphenoid bone.

14. CHONDROCRANIUM (3) TRABECULAE CRANII (3) TRABECULAE CRANII They fuse to form the body of the ethmoid. They fuse to form the body of the ethmoid. (4) ALA ORBITALIS (4) ALA ORBITALIS It forms the lesser wing of the sphenoid. It forms the lesser wing of the sphenoid. (5) ALA TEMPORALIS (5) ALA TEMPORALIS It forms the greater wing of the sphenoid. It forms the greater wing of the sphenoid.

15. CHONDROCRANIUM (6) OTIC CAPSULES (6) OTIC CAPSULES They surround the otic vesicles (primordia of the internal ear). They surround the otic vesicles (primordia of the internal ear). They form the petrous and mastoid parts of the temporal bone. They form the petrous and mastoid parts of the temporal bone.

16. CHONDROCRANIUM (7) NASAL CAPSULES (7) NASAL CAPSULES They surround the nasal sacs and contribute to the formation of the ethmoid bone. They surround the nasal sacs and contribute to the formation of the ethmoid bone.

17. CARTILAGENOUS NEUROCRANIUM An elongated median plate of cartilage is formed between the nasal region and the anterior border of the foramen magnum. An elongated median plate of cartilage is formed between the nasal region and the anterior border of the foramen magnum.

18. OSSIFICATION It begins in the: It begins in the: 1. Occipital bone 1. Occipital bone 2. Basisphenoid (body of sphenoid) bone. 2. Basisphenoid (body of sphenoid) bone. 3. Ethmoid bone. (In that order). 3. Ethmoid bone. (In that order).

19. VISCEROCRANIUM The mesenchyme forming the bones of the face including the nasal and lacrimal bones is derived from the Neural Crest cells that migrate into the first two pharyngeal arches. The mesenchyme forming the bones of the face including the nasal and lacrimal bones is derived from the Neural Crest cells that migrate into the first two pharyngeal arches.

20. 1 ST ARCH The Dorsal end of the first arch (Meckel ’ cartilage) forms: The Dorsal end of the first arch (Meckel ’ cartilage) forms: The bony ossicles of the middle ear The bony ossicles of the middle ear (Malleus and Incus). (Malleus and Incus). Its remnant is the Sphenomandibular ligament. Its remnant is the Sphenomandibular ligament..

21. 2 ND ARCH The (Dorsal) end of the Second arch (Reichert ’ cartilage) forms : The (Dorsal) end of the Second arch (Reichert ’ cartilage) forms : 1. Stapes of the middle ear. 1. Stapes of the middle ear. 2. Styloid process of the temporal bone. 2. Styloid process of the temporal bone.

22. 2 ND ARCH The (Ventral) end of the 2 nd arch forms : The (Ventral) end of the 2 nd arch forms : 1.Lesser horn. 1.Lesser horn. 2. Superior part of the (body of hyoid bone). 2. Superior part of the (body of hyoid bone).

23. 3 RD ARCH The (Ventral) part of the 3 rd arch forms: The (Ventral) part of the 3 rd arch forms: 1. Greater horn. 2.Inferior part of the (body of hyoid). 1. Greater horn. 2.Inferior part of the (body of hyoid).

24. 4 TH & 6 TH ARCHES They fuse to form They fuse to form the Laryngeal cartilages Except the Epiglottis. the Laryngeal cartilages Except the Epiglottis.

25. MEMBRANOUS VISCEROCRANIUM Intramembranous ossification of the Maxillary prominence (dorsal portion of the first arch ) gives the following bones: Intramembranous ossification of the Maxillary prominence (dorsal portion of the first arch ) gives the following bones: 1. Squamotemporal (becomes part of the neurocranium). 1. Squamotemporal (becomes part of the neurocranium). 2. Maxilla. 2. Maxilla. 3. Zygomatic. 3. Zygomatic.

26. MANDIBLE It is formed from It is formed from Intramembranous ossification of the Mandibular prominence (ventral portion of the first arch). Intramembranous ossification of the Mandibular prominence (ventral portion of the first arch). Endochondral ossification : Endochondral ossification : The mandibular condyles and the median plane The mandibular condyles and the median plane

27. SKULL OF NEW BORN It is large in proportion to the rest of the skeleton. It is large in proportion to the rest of the skeleton. Small face is due to: Small face is due to: 1. Small size of the jaws. 1. Small size of the jaws. 2. Absence of the Para nasal sinuses. 2. Absence of the Para nasal sinuses. 3. Underdeveloped facial bones at birth. 3. Underdeveloped facial bones at birth.

28. POST NATAL GROWTH OF THE SKULL The greatest increase of size of the calvaria is during the first two years. This is the period of most rapid increase of size of the brain. The greatest increase of size of the calvaria is during the first two years. This is the period of most rapid increase of size of the brain. The calvaria normally increases in capacity until about 16 years of age. The calvaria normally increases in capacity until about 16 years of age. A slight increase of its size for 3 to 4 years because of increase thickening of the bone. A slight increase of its size for 3 to 4 years because of increase thickening of the bone.

29. CRANIOSYNOSTOSIS It is premature closure of the skull sutures. It is premature closure of the skull sutures. Its cause is unknown but genetic factors are important it is more common in males. Its cause is unknown but genetic factors are important it is more common in males.

30. (1) SCAPHOCEPHALY Premature closure of the Sagittal suture. Premature closure of the Sagittal suture. The skull becomes long, narrow and wedge- shaped. The skull becomes long, narrow and wedge- shaped.

31. (2) OXYCEPHALY Premature closure of the Coronal suture. Premature closure of the Coronal suture. The skull is high and tower like. The skull is high and tower like.

32. (3) PLAGIOCEPHALY (3) PLAGIOCEPHALY Premature closure of the Coronal or Lambdoid sutures. Premature closure of the Coronal or Lambdoid sutures. The skull is twisted and asymmetric. The skull is twisted and asymmetric.