Anatomy of the Canine Spine

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Introduction

The anatomy of the canine spine is almost similar to the human spine. The spine of the canine also 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, 3 sacral vertebrae and the number of caudal vertebrae varies according to the species.

Cervical spine

Atlas and axis are the first two cervical vertebrae respectively.

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 is the one that holds the dens of the axis against the ventral arch of the atlas.

Axis is the second cervical vertebra and is the longest vertebra. The atlantoaxial joint is the 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.

Nuchal ligament is a paired band of connective tissue that spinous process of cervical vertebrae to the spinous process of thoracic vertebra (from axis to T1). The ligamentum flavum, dorsal longitudinal ligament and ventral longitudinal ligament are similar to that of human being. The ligamentum flavum connects the lamina of adjacent lamina. The anterior longitudinal ligament attaches to the front of each vertebra and posterior longitudinal ligament runs at 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 namely 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: rsal 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 spine

The thoracic vertebrae differs from other vertebrae due to it's distinct feature. The thoracic vertebrae articulates with the rib that corresponds in the number. It has short bodies and flattened extremities. It has short articular processes and the long spinous process. The caudal articular processes of the thoracic vertebrae face ventrally and at the base of spinous process whereas the cranial articular processes of the thoraic vertebrae are oval facets on arch of vertebrae and face dorsally. All the thoracic vertebrae has a pair of costal facets on 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 a point at which vertebral anatomic features change and the spinous process becomes perpendicular to the body and the preceeding vertebra incline caudally.

The costovertebral joint has two artculation between rib and the vertebral column