Skeletal System: Axial and Appendicular Skeleton Study Notes

Bone Markings refer to specific anatomical features of bones, described as follows:
- Articulating surfaces:
- Condyle: Large, smooth, rounded, oval structure.
- Facet: Small, flat, shallow surface.
- Head: Prominent, rounded epiphysis.
- Trochlea: Smooth, grooved, pulleylike process.
- Depressions:
- Alveolus (pl., alveoli): Deep pit or socket in the maxillae or mandible.
- Fossa (pl., fossae): Flattened or shallow depression.
- Sulcus: Narrow groove.
- Projections:
- Crest: Narrow, prominent, ridgelike projection.
- Epicondyle: Projection adjacent to a condyle.
- Line: Low ridge.
- Process: Any marked bony prominence.
- Ramus (pl., rami): Angular extension of a bone relative to the rest of the structure.
- Spine: Pointed, slender process.
- Trochanter: Massive, rough projection found only on the femur.
- Tubercle: Small, round projection.
- Tuberosity: Large, rough projection.
- Openings and Spaces:
- Canal: Passageway through a bone.
- Fissure: Narrow, slitlike opening through a bone.
- Foramen (pl., foramina): Opening or hole in a bone.
- Meatus: Passageway through a bone.
- Sinus: Cavity or hollow space in a bone.

Anterior View:
- Frontal Bone: Forehead region.
- Lateral Growth: Left and Right Orbits consists of multiple skull bones.
- Two openings:
- Superior Orbital Fissure
- Inferior Orbital Fissure
- Other Features:
- Superciliary Arches: Brow ridges, larger in males.
- Nasal Bones: Form bony bridge of nose.
- Maxillae: Form upper jaw, lateral boundaries of nasal cavity.
- Mandible: Forms lower jaw, identified by the mental protuberance.
- Inferior Nasal Spine: Marks inferior border of nasal cavity.
- Nasal Septum: Divides nasal cavity into left and right halves.
- Inferior Nasal Conchae: Two scroll-shaped bones on the inferolateral walls of nasal cavity.
Superior View:
- Shows four cranial bones:
- Frontal, Parietal (both left and right), Occipital.
- Sutures:
- Coronal Suture: Between Frontal and Parietal bones.
- Sagittal Suture: Between the left and right parietal bones.

Sutures: Immovable joints forming boundaries between cranial bones.
- Coronal Suture: Between frontal and parietal bones, extends laterally across the superior surface of the skull.
- Lambdoid Suture: Between parietal bones and occipital bone, resembles the Greek letter “lambda”.
- Sagittal Suture: Articulation between right and left parietal bones, extends between coronal and lambdoid sutures.
- Squamous Suture: Articulation between temporal bone and parietal bone on each side.
- Sutural Bones (Wormian Bones): Independent ossification centers, most common in lambdoid suture.

Auditory Ossicles: Composed of 3 tiny ear bones located within the petrous part of each temporal bone:
- Malleus
- Incus
- Stapes
Hyoid Bone: A slender, curved bone below the skull between the mandible and larynx.
- Functions as an attachment site for muscles and ligaments of the tongue and larynx.

Sexual Dimorphism: Variations between female and male skulls.
- Female Skull Features: Generally more delicate and smaller.
- Male Skull Features: Larger and bulkier.
- Structural features vary across populations.
- Determining genetic sex in infants and juveniles is challenging due to gradual density changes post-puberty.

Vertebral Column: Important for maintaining an upright position, housing and protecting the spinal cord, and supporting the weight of the head.
- Composed of:
- 24 Individual Vertebrae.
- Fused vertebrae of Sacrum and Coccyx (total varies but typically 33).
- Divisions:
- Cervical: 7 vertebrae (C1–C7).
- Thoracic: 12 vertebrae (T1–T12).
- Lumbar: 5 vertebrae (L1–L5).
- Sacrum: Formed from 5 fused sacral vertebrae (S1–S5).
- Coccyx: Composed of 4 coccygeal vertebrae (Co1–Co4).

4 Spinal Curvatures classified as:
- Primary Curves: Thoracic and Sacral (present at birth).
- Secondary Curves: Cervical and Lumbar (develop after birth).
- Cervical curve appears as children gain head control (3-4 months).
- Lumbar curve develops when standing and walking begins (by first year of life).

Common Structural Features of Vertebrae:
- Body: Thick anterior structure for weight bearing.
- Vertebral Arch: Forms posterior enclosure around vertebral foramen (opening for the spinal cord).
- Vertebral Canal: Formed by stacked vertebral foramina, housing the spinal cord.
- Intervertebral Foramina: Lateral openings between adjacent vertebrae for spinal nerves.
- Vertebral Arch Composition:
- 2 Pedicles and 2 Laminae.
- Pedicles originate from the body.
- Laminae extend to the spinous process.

Thoracic Cage: Framework of the chest.
- Consists of:
- Thoracic Vertebrae (posteriorly).
- Ribs (laterally).
- Sternum (anteriorly).
- Function: Protective enclosure around thoracic organs; attachment sites for muscles.

Similarities:
- Upper and lower limbs share common evolutionary features but differ in structure for specific functions.
- Each limb has one large proximal bone and two distal bones.
- Distal parts have multiple bones for flexibility.
Structural Differences:
- Lower limb is weight bearing, casting some mobility for more stability.
- Upper limb is not primarily weight bearing, allowing for diverse movements.

Students should review various tables detailing bones included in both the axial and appendicular skeletons and memorize distinguishing features of each bone according to the formats outlined in this material. Additionally, the text offers insights into potential pathologies and developmental conditions associated with skeletal structures, aiding in clinical understanding and applied anatomy.