📝 STANDARD DESCRIPTION:
Type: Extrinsic, Superficial Layer
Origin: Nuchal ligament (C2-Thoracic inlet) [Cervical part]; Supraspinous ligament (T2-T10/12) [Thoracic part]
Insertion: Scapular spine (cervical part along dorsal length; thoracic part on dorsal third)
Function: Elevates shoulder; cervical part protracts (draws craniodorsally), thoracic part retracts (draws caudodorsally).
📚 DETAILED DESCRIPTION:
SUPERFICIAL SHOULDER SUSPENSION SYSTEM
The trapezius is a broad triangular sheet classified as the primary extrinsic elevator and abductor of the scapula. Unlike equines where the separation is more distinct, the bovine trapezius is divided into two parts by a tendinous aponeurosis.
FIBER ARCHITECTURE:
• Pars Cervicalis (Cranial): Originates from the funicular nuchal ligament extending from the axis (C2) to the thoracic inlet. Fibers run caudoventrally.
• Pars Thoracica (Caudal): Originates from the supraspinous ligament of thoracic vertebrae (T2 to T10 or T12). Fibers run cranioventrally.
• Both parts converge on the scapular spine, creating a force-coupling mechanism for multidirectional control.
BIOMECHANICAL DYNAMICS:
When acting unilaterally in the non-weight-bearing limb, the cervical component draws the scapula craniodorsally (protraction), assisting the forward swing phase. The thoracic component draws the scapula caudodorsally (retraction). When acting bilaterally, they fix the scapula against the trunk, providing stability during weight bearing and shock absorption.
NEURAL SUPPLY: Dorsal branch of the Accessory nerve (Cranial Nerve XI). Damage leads to shoulder drooping and atrophy, though true clinical 'Sweeny' typically involves the suprascapular nerve.
// COMPARATIVE ANALYSIS
| HORSE |
Separation between cervical and thoracic parts is much more distinct; cervical part originates from C2-C7. |
| DOG |
Divided into cervical, thoracic, and lumbar parts; more extensive origin. |
CLINICAL RELEVANCE
Accessory Nerve Injury: Damage in the cervical region leads to shoulder atrophy and depression, though less common than suprascapular neuropathy for instability.
