Anatomy of the Canine Spine

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Introduction

The anatomy of the canine spine is quite similar to the human spine. Like in people, the canine spine supports weight and encloses the spinal cord. The spine is located along the dorsal/top side of the canine's body and runs from the base of the head to the end of the tail.

The canine spine is divided into five regions: cervical, thoracic, lumbar, sacral, and caudal. There are 7 cervical vertebrae, 13 thoracic vertebrae, 7 lumbar vertebrae and 3 sacral vertebrae. The number of caudal vertebrae varies according to the species.

Joints and Ligaments of the Skull

Temporo-mandibular joint:

• A condylar joint, with an articular disc, that sits between the mandibular condyles and the mandibular fossa of the temporal bones
• It has a loose joint capsule with thickening which forms a lateral ligament has an
• The temporals muscle closes the jaw and the joint is innervated by cranial nerve V

Mandibular symphysis

Joints of the hyoid apparatus:

• Tympanohyoid cartilage - skyll (a syndesmosis joint)
• Interhyoid joints (synovial joints)
• Thyrohyoid bone - cranial cornu of thyroid cartilage (synovial joint)

Anatomy of canine spine

Cervical vertebrae

The atlas and axis are cervical vertebrae 1 and 2.

The atlanto-occipital joint is a condylar modified synovial hinge joint. The capsule of the joint is strengthened by three thickenings: dorsal, ventral, and lateral. The transverse process of the atlas is the wing that allows the articulation of the occipital condyles and the spine.The atlas and axis are fused in embryonic life. The transverse atlantal ligament holds the dens of the axis against the ventral arch of the atlas.

The axis is the second and longest cervical vertebra. The atlantoaxial joint is a pivot joint and has a loose joint capsule. The dens of the axis is connected to the occipital bone through the apical ligament.

The cervical vertebrae are obliquely oriented in the transverse plane. The cranial articular processes face dorsomedially whereas the caudal articular processes face ventrolaterally.

The nuchal ligament is a paired band of connective tissue that connects the spinous processes of cervical vertebrae to the spinous processes of thoracic vertebra (from C1 to T1). The canine ligamentum flavum, dorsal longitudinal ligament and, ventral longitudinal ligament are similar to those in people:

• The ligamentum flavum connects the lamina of adjacent lamina
• The anterior longitudinal ligament attaches to the front of each vertebra
• The posterior longitudinal ligament runs along the posterior aspect of spine and inside of the spinal cord

Muscles of the cervical spine (table extracted from a presentation of Ansi Van Der Walt )

Muscle	Origin	Insertion	Innervation	Action
Omotransversarius	Lower spine of scapula	Wing of atlas	Ventral branches of local cervical spinal nerve	Advances limb Moves neck laterally
Brachiocephalicus	The clavicle divides the muscle into two: cleidobrachialis and cleidomastoideus
Cleidobrachialis	Clavicular intersection	Crest of the humerus	Axillary nerve	Advances limb Adducts Limb
Cleidomastoideus	Clavicular intersection	Mastoid process of the temporal bone	Ventral branch of the accessory nerve (cranial nerve XI)	Forms dorsal border of jugular groove Advances limb Flexes neck Turns head
Sternocephalicus (sternomandibularis)	Manubrium of the sternum	Mastoid part of temporal bone Nuchal crest	Ventral branch of Accessory nerve (Cranial nerve XI)	Forms ventral border of jugular groove Flexes neck Turns head Opens mouth
Omohyoideus	Subscapular Fascia	Lingual process of basihyoid bone	Spinal nerve C1	Forms medial border of jugular groove Retracts basihyoid bone and tongue
Trapezius (cervical and thoracic parts)	Nuchal ligament and supraspinous ligament of C2-10	Cervical part: entire scapular spine Thoracic part: dorsal third of scapular spine	Dorsal branch of accessory nerve (cranial nerve XI)	Advances thoracic limb Abducts thoracic limb Elevates shoulder
Rhomboiudeus muscle (cervical and thoracic)	Nuchal ligament and dorsoscapular ligaments of C2-T8	Scapular cartilage	Local thoracic nerve Local cervical nerve	Elevates neck Draws scapula cranially and dorsally
Serratus ventralis cervicis	Transverse processes of C4-7	Scapular cartilage and medial scapula	Ventral branches of local cervical nerve	Supports trunk between forelimbs Raises neck when the limb is fixed
Splenius (capitis and cervicis)	Nuchal ligament and spinous processes of T3-5 via the thoracolumbar fascia	Nuchal crest and the mastoid process of temporal bone	Dorsal branch of accessory nerve (cranial nerve XI) and dorsal branch of local spinal nerve	Extends neck Elevates neck Bends neck laterally
Longissimus (cervicis,capitis, atlantis)	Transverse processes of cervical and thoracic vertebrae	Wing of atlas and mastoid process of temporal bone	Dorsal branches of local spinal nerve	Elevates head and neck Bends head and neck laterally Stabilizes and extends vertebral column
Semispinalis capitis	Articular processes of C2/3-7 and transverse processes of T1-6/7	Occipital bone	Dorsal branches of local spinal nerve	Elevates head and neck Bends head and neck laterally
Longus capitis	Transverse processes of C3-5	Mastoid process	Ventral branch of local spinal nerve
Longus colli
cervical part	Transverse processes of C3-7	Ventral tubercle of atlas and bodies of cervical vertebrae	Ventral branches of local spinal nerve	Flexes head
thoracic part	Bodies of T1-6	Transverse processes of C6-7	Ventral branches of local spinal nerve	Flexes head Bends head laterally
Obliquus capitis caudalis	Spinous process of the axis	Wings of the atlas	Dorsal branch of C2	Rotates atlas and head
Rectus capitis dorsalis muscle
major	Spinous process of the axis	Nuchal crest	Dorsal branch of C1	Elevates head
minor	Dorsal arch of the atlas	Occipital bone	Dorsal branch of C1	Elevates head
Scalenes (composed of two unequal parts and the lower one is larger)	From the transverse process of the last four cervical vertebrae	Into the anterior border and outer surface of the first rib		Assists inspiration by drawing the first rib forward With rib fixed draws the neck downward and to one side

Thoracic vertebrae

The thoracic vertebrae differ from other vertebrae in a number of ways. The thoracic vertebrae articulate with the corresponding rib (i.e. T1 to rib 1). Each thoracic vertebra has a short body, flattened extremities, short articular processes and a long spinous process. The caudal articular processes of the thoracic vertebrae face ventrally and are at the base of the spinous process. The cranial articular processes of the thoracic vertebrae are oval facets on the arch of vertebrae and face dorsally. All thoracic vertebrae have a pair of costal facets on the dorsal body (except T13) forming costal fovea. There are costal facets on the transverse processes of the vertebrae and cranial and caudal fovea on the extremities of the vertebral bodies. The 11th thoracic vertebra is also known as the anticlinal vertebra. The anticlinal vertebra is the point at which vertebral anatomic features change and the spinous process becomes perpendicular to the body and the preceding vertebra incline caudally.

The costovertebral joint has two articulations between the rib and the vertebral column. The head of the rib articulates with the cranial and costal facets of the adjacent vertebrae and is a ball and socket synovial joint. Similarly, the tubercle of the rib articulates with the transverse process of the vertebra and is a plane synovial joint. The ligaments of the costovertebral joint are the radiate ligament of the head, inter capital ligament (connects the head of the pair of opposite rib), costotransverse ligaments and ligament of the neck.

Lumbar spine

lumbar vertebrae are more uniform and longer in shape than the thoracic vertebrae. The cranial articular process of the lumbar spine is fused with the mamillary processes and the articular processes are concave dorsally and mostly in sagittal alignment. The caudal processes are convex ventrally and correspond with the convexity of cranial articular processes. The lumbar vertebrae are differentiated from the thoracic vertebrae by their lack of costal facets. The lumbar spine allows the flexion and extension of the spine. Lateral flexion and rotation are very limited especially at the L4-L5 due to the intertransverse joints.

Ligaments of the thoracolumbar joint

• The dorsal longitudinal ligament forms a part of the floor of the vertebral canal from the axis to the sacrum and prevents hyperflexion of the spine
• An interspinous ligament connects the spines of adjacent vertebrae from the axis to the sacrum
• Intertransverse ligament
• Interarcuate ligament / ligamentum flavum / yellow ligaments are the elastic ligaments filling dorsal spaces between the arches of adjacent vertebrae
• The supraspinous ligament is made up of heavy bands of the connective tissue that run over the top of the spinous processes (T2/T3 caudally). This ligament prevents abnormal separation of spinous processes during flexion of the spine. The supraspinous ligament is a direct continuation of the funicular part of the nuchal ligament.
• Ventral longitudinal ligament runs ventrally from axis to sacrum and widens caudally.This prevents hyperextension of the spine and is at its strongest in the lumbar spine

Sacral vertebrae

The sacrum is formed by the fusion of the sacral vertebrae and articulates with the pelvic girdle.The sacrum narrows and forms a curve caudally and forms a concave surface for the pelvic cavity.

Caudal vertebrae

The number of caudal vertebrae differs from species to species.

Muscles of the trunk (table extracted from a presentation of Ansi Van Der Walt

Muscle	Origin	Insertion	Innervation	Action
Lattisimus dorsi	Supraspinous ligament from T3 and thoracolumbar fascia	Teres major tuberosity of humerus	Thoracodorsal nerve	Flexes shoulder and draws limb caudally Draws trunk cranially when limb is flexed
Serratus ventralis thoracis	Ribs 1-8/9	Scapular cartilage and medial scapula	Long thoracic nerve	Supports trunk between forelimbs Raises neck when limb is flexed
Serratus dorsalis
cranialis	Supraspinous ligament	Cranial border of ribs 5-11	Intercostal nerve	Muscle of inspiration
caudalis	Thoracolumbar fascia	Caudal border of ribs 11-13	Intercostal nerve	Muscle of expiration
External intercostal muscles	Muscles run caudodorsally in the intercostal spaces		Intercostal nerve	Muscles of inspiration
Internal intercostal muscles	Muscles run craniodorsally in the intercostal spaces		Intercostal nerve	Muscles of expiration
External abdominal oblique muscle	Thoracolumbar fascia and lateral aspect of ribs 4-13	Linea alba Prepubic tendon Pelvic tendon Coxal tuber Inguinal ligament	Ventral branches of lumbar nerve and local intercostal nerve	Abdominal press Flexes the trunk
Internal abdominal oblique muscle	Coxal tuber and inguinal ligament	Linea alba, Prepubic tendon last rib Cartilages of ribs 14-18	Ventral branches of lumbar nerve and local intercostal nerve	Abdominal press Flexes the trunk
Transversus abdominis	Medial surface of costal cartilages 7-18 and transverse processes of lumbar vertebrae	Linea alba	Ventral branches of lumbar nerve and lumbar intercostal nerve	Abdominal press Flexes the trunk
Rectus abdominis	lateral surface of costal cartilages 4-9	Prepubic tendon and head of the femur (via accessory ligament)	Ventral branches of lumbar nerve and local intercostal nerve	Abdominal press Flexes the trunk Flexes lumbar spine and lumbosacral joint
Longisimus thoracis and lumborum	Spinous processes of thoracic, lumbar and sacral vertebrae and wings of illium	Transverse processes of vertebrae and tubercles of rib	Dorsal branches of lumbar nerve	Stabilises and extends vertebral column
Semispinalis thoracis and lumborum	From the sacrum and from the articular processes of the lumbar vertebrae and from the transverse processes of the dorsal vertebrae	Each slip inserts into the spinous process of the third or fourth vertebra in front of the one from which it arises	Dorsal branches of local spinal nerve	To fix the bones during the action of the large spinal muscles, and to assist in extending the spine
Iliocostalis thoracis and lumborum	Runs obliquely between the transverse processes of the vertebrae to the bodies of the adjacent vertebrae and/or the tuberosities of the rib		Dorsal branches of local spinal nerves	Expiration Thoracolumbar extension
Cutaneous trunci	Superficial trunk fascia (from the withers to the fold of the flank)	Superficial shoulder fascia and medial surface of the humerus	Lateral thoracic nerve and intercostobrachial nerve	Moves the skin of the abdomen (and the trunk )
Longissimus thoracis and lumborum muscle are continuous from pelvis through thorax	Spinous processes of thoracic, lumbar and sacral vertebrae and wings of illium	Transverse processes of vertebrae and tubercles of ribs	Dorsal branches of local spinal nerve	Stabilises and extends vertebral column
Multifidus lumborum muscle (continuous with thoracis and cervicis)	Articular processes of each vertebra from C2 to sacrum	Spinous process of the preceding vertebra	Dorsal branches of local spinal nerve	Stabilises vertebral column Rotates vertebral column
Psoas major muscle Part of iliopasoas muscle	Lumbar transverse processes and ventral surface of last two ribs	Lesser trochanter of femur (as fused iliopsoas muscle)	Ventral branches of lumbar and local intercostal nerve and lumbar plexus	Rotates pelvic limb outwards Flexes hip and advances limb Stabilises vertebral column when limb is fixed