The Vertebral Column and Spine Anatomy

The Spine

• The spine is the central bony pillar of the body, supporting the skull, pectoral girdle, upper limbs, thoracic cage, and pelvis
• The spine is composed of 33 vertebrae: 7 cervical, 12 thoracic, 5 lumbar, 5 sacral (fused to form the sacrum), and 4 coccygeal
• Intervertebral discs, made of fibrocartilage, are flexible structures between the vertebrae, forming about one quarter of the spine's length

Characteristics of a Vertebra

• A typical vertebra consists of a rounded body anteriorly and a vertebral arch posteriorly, enclosing the vertebral foramen
• The vertebral arch is formed by a pair of cylindrical pedicles and laminae, which complete the arch posteriorly

Thoracic Vertebrae

• The body of a typical thoracic vertebra is medium-sized and heart-shaped
• The vertebral foramen is small and circular
• The spines are long and inclined downward
• Costal facets are present on the sides of the bodies for articulation with the heads of the ribs

Lumbar Vertebrae

• The body of a typical lumbar vertebra is large and kidney-shaped
• The pedicles are strong and directed backward
• The laminae are short in a vertical dimension
• The vertebral foramina are triangular
• The transverse processes are long and slender
• Lumbar vertebrae have no facets for articulation with ribs and no foramina in the transverse processes

Sacrum

• The sacrum consists of five rudimentary vertebrae fused together to form a wedge-shaped bone
• The sacrum articulates with the two iliac bones to form the sacroiliac joints
• The vertebral foramina are present and form the sacral canal, which contains the anterior and posterior roots of the sacral and coccygeal spinal nerves

Coccyx

• The coccyx consists of four vertebrae fused together to form a single, small triangular bone
• The first coccygeal vertebra is usually not fused or is incompletely fused with the second vertebra

The Orbital Region

• The orbit is a pyramidal cavity with its base anterior and its apex posteriorly
• The orbital margin is formed by the frontal bone, the lateral margin by the processes of the frontal and zygomatic bones, the inferior margin by the zygomatic bone and the maxilla, and the medial margin by the processes of the maxilla and the frontal bone
• The roof is formed by the orbital plate of the frontal bone, which separates the orbital cavity from the anterior cranial fossa
• The lateral wall is formed by the zygomatic bone and the greater wing of the sphenoid
• The floor is formed by the orbital plate of the maxilla, which separates the orbital cavity from the maxillary sinus
• The medial wall is formed by the frontal process of the maxilla, the lacrimal bone, the orbital plate of the ethmoid, and the body of the sphenoid

Openings into the Orbital Cavity

• Supraorbital notch (foramen): transmits the supraorbital nerve and blood vessels
• Infraorbital groove and canal: transmits the infraorbital nerve and blood vessels
• Nasolacrimal canal: transmits the nasolacrimal duct
• Inferior orbital fissure: transmits the maxillary nerve and its zygomatic branch, the inferior ophthalmic vein, and sympathetic nerves
• Superior orbital fissure: transmits the lacrimal, frontal, and nasociliary branches of the ophthalmic division of the trigeminal nerve, trochlear, oculomotor, and abducent nerves, and the superior ophthalmic vein
• Optic canal: transmits the optic nerve and the ophthalmic artery
• Anterior ethmoidal foramen: transmits the anterior ethmoidal nerve and vessels
• Posterior ethmoidal foramen: transmits the posterior ethmoidal nerve and vessels
• Zygomatic foramen (1 or 2 openings): transmits the zygomatic branches

Nasal Cavity

• The nasal vestibule is the area of the nasal cavity lying just inside the nostril
• The nasal cavity is divided into right and left halves by the nasal septum
• The septum is made up of the septal cartilage, the vertical plate of the ethmoid, and the vomer
• The floor of the nasal cavity is formed by the palatine process of the maxilla and the horizontal plate of the palatine bone
• The roof is narrow and is formed anteriorly beneath the bridge of the nose by the nasal and frontal bones
• The lateral wall of each nasal cavity mainly consists of the maxilla, palatine bone, medial pterygoid plate, labyrinth of ethmoid, inferior concha, and lacrimal bone

Hyoid Bone

• The hyoid bone is a mobile single bone found in the midline of the neck below the mandible and above the larynx
• The hyoid bone is U-shaped and consists of a body and two greater and two lesser cornua
• It is attached to the skull by the stylohyoid ligament and to the thyroid cartilage by the thyrohyoid membrane
• It connects to the mandible, styloid process of the temporal bone, thyroid cartilage, sternum, and scapula through various muscles