Skull Bones and Sutures

Bones of the Skull

• Separate bones unite at immobile joints called sutures because of the sutural ligament
• Sutures become obliterated later in life
• The skull consists of the calvaria and the facial skeleton
• The cranium refers to the skull without the mandible

Skull Bones

• Flat bones form external and internal tables of compact bone
• Bones divide by diploe
• Periosteum covers the outer and inner bone surfaces

Cranium bones

• The cranium includes:
  • 1 Frontal bone
  • 2 Parietal bones
  • 1 Occipital bone
  • 2 Temporal bones
  • 1 Sphenoid bone
  • 1 Ethmoid bone

Facial Bones

• The facial skeleton includes:
  • 2 Zygomatic bones
  • 2 Maxillae
  • 2 Nasal bones
  • 2 Lacrimal bones
  • 1 Vomer
  • 2 Palatine bones
  • 2 Inferior conchae
  • 1 Mandible

Norma Verticalis Bones

• Norma verticalis has 4 bones: one frontal, one occipital, and two parietal bones
• Coronal sutures run between the frontal bone and two parietal bones
• The sagittal suture runs in the midline between the two parietal bones
• Lambdoid suture runs between the two parietal bones and the occipital bone

Bregma and Lambda

• Bregma is the point where the coronal and sagittal sutures meet
• Before ossification, the bregma is a gap filled with the anterior fontanelle membrane
• Bregma ossifies 18 months following birth
• Lambda marks the meeting point of sagittal and lambdoid sutures
• Before ossification, the lambda is a gap filled with the posterior fontanelle membrane in the fetus and up to 3 months after birth

Norma Frontalis

• Norma frontalis is formed by 1 frontal, 2 nasal, 2 maxilla, 2 zygoma, vomer, the inferior concha, and the mandible
• Features 2 orbits, 2 anterior nasal openings, and an oral opening
• Sutures include: frontonasal, internasals, fronto-maxillary, nasomaxillary, intermaxillary, frontozygomatic, zygomaticomaxillary

Forehead

• The forehead is part of norma frontalis, is formed by the frontal bone
• Features include: superciliary arches, glabella, frontal eminence, and nasion.
• Naison is the meeting point of internasal and frontonasal sutures

Orbital Opening

• Orbital opening has 4 margins
• The supraorbital margin shows the supraorbital notch
• The lateral margin includes: the frontal process of the zygomatic bone and the zygomatic process of the frontal bone
• The infraorbital margin has the maxilla and zygomatic bones, and contains the infraorbital foramen
• The medial margin includes the frontal process of the maxilla and the maxillary process of the frontal bone

Anterior Nasal Aperture

• Pear-shaped and bounded by 2 nasal bones and 2 maxillae
• Includes the anterior nasal spine

Maxilla (Norma Frontalis)

• Maxilla forms the boundaries of the anterior nasal aperture and the superior alveolar process
• The anterior surface includes the infraorbital foramen and the canine eminence

Prominence of the Cheek

• Formed by Zygomatic Bone
• Its anterior surface shows the zygomatico-facial foramen

Norma lateralis

• Located on the upper skull above the zygomatic arch
• Has following boundaries: frontal process of zygomatic bone; temporal line; supramastoid crest; zygomatic arch
• The Frontal part shows H-shaped suture (pterion)

Pterion Formation

• Formed by
  • Frontal bone
  • Parietal bone
  • Squamous part of the temporal bone
  • Greater wing of sphenoid

Temporal Fossa

• Separates the fossa from the cranial cavity
• Communicates with infratemporal fossa deep to zygomatic arch
• Anterior wall shows zygomaticotemporal foramen

Temporal Line

• Includes:
  • the zygomatic process of the frontal bone
  • the superior and inferior temporal lines
  • the supramastoid crest
• Zygomatic Arch formed by:
  • the temporal process of the zygomatic bone
  • the zygomatic process of the temporal bone

External Acoustic Meatus

• Consists of
• The squamous part of the temporal bone above
• Tympanic bone in front, below and behind

Mastoid Part Of Temporal Bone

• Articulates with:
  • Parietal bone: the Parietomastoid suture
  • Occipital bone: the Occipitomastoid suture,
• Behind the external acoustic meatus

Infratemporal Fossa

• The space below the temporal fossa and separated by the zygomatic arch
• With has the following Boundaries:
  • Roof: the infratemporal surface of the greater wing of the sphenoid
  • Anterior wall: the back of the maxilla
  • Medial wall: the lateral pterygoid plate
  • Lateral wall: the ramus of mandible
• Pterygomaxillary Fissure leads to the Pterygopalatine fossa

Norma Occipitalis

• Composed of the lambdoid suture between the 2 parietal bones at the front and the squamous portion of the occipital bone behind
• Features include:
  • the external occipital protuberance which lies midline
  • the superior nuchal lines that extend from the external occipital protuberance transversely
  • the highest muchal line, that lies 1 cm above and parallel to the superior nuchal line