📝 STANDARD DESCRIPTION:
Superficial Neck Muscles:
• Brachiocephalicus — long muscle from skull → arm; flexes/extends neck, advances limb.
• Sternomandibularis (Sternocephalicus mandibular part) — sternum to mandible; flexes head.
• Sternocephalicus (mastoid part) — sternum to mastoid; turns head sideways.
• Omotransversarius — scapula to wing of atlas.
• Splenius, Rhomboideus, Longissimus capitis — deeper neck muscles.
Jugular Furrow Boundaries:
• Cranial: caudal border of mandible.
• Caudal: manubrium sterni.
• Dorsal: brachiocephalicus muscle.
• Ventral: sternocephalicus (mandibular part) — sternomandibularis.
• Floor: deep cervical fascia / scalene + omohyoid.
• Contents: External jugular vein (the practical IV site in cattle/horse).
📚 DETAILED DESCRIPTION:
NECK MUSCLES & JUGULAR FURROW
The neck has multiple layers of muscles classified by function: head/neck movement, limb advancement, and respiratory accessory.
I. SUPERFICIAL LATERAL MUSCLES:
1. Brachiocephalicus:
• Long strap-like muscle from base of skull (mastoid + occipital) to crest of greater tubercle of humerus.
• 3 parts in domestic mammals — cleidomastoideus + cleido-occipitalis + cleidobrachialis (the clavicle is a tendinous intersection in domestic species).
• Action: Advances limb, extends shoulder, turns head/neck.
• Forms the DORSAL boundary of the jugular furrow.
2. Sternocephalicus:
• Two parts: Sternomandibularis (to mandible) and Sternomastoideus (to mastoid process).
• Origin: manubrium sterni.
• Action: Flexes neck, turns head.
• Forms the VENTRAL boundary of the jugular furrow.
3. Omotransversarius: Wing of atlas → scapula. Advances limb.
II. JUGULAR FURROW (Sulcus jugularis):
• Distinct groove on the lateral surface of the neck.
• Cranial limit: caudal border of mandible / parotid region.
• Caudal limit: shoulder / manubrium sterni.
• Dorsal wall: brachiocephalicus.
• Ventral wall: sternocephalicus (mandibular).
• Floor (deep): scalene & longus colli muscles + carotid sheath.
• Contents:
– External jugular vein (most superficial — the venepuncture target).
– Deep to the vein: Common carotid artery, Vagosympathetic trunk, Recurrent laryngeal nerve, Tracheal duct = these together form the CAROTID SHEATH.
III. CAROTID SHEATH:
A connective tissue tube that wraps and binds the deep cervical neurovascular bundle:
• Common carotid artery — to head.
• Internal jugular vein (small in horse, may be absent).
• Vagosympathetic trunk — vagus + sympathetic combined.
• Recurrent laryngeal nerve — ascends from thorax along trachea-oesophagus groove.
Important during deep neck surgery; accidental injury produces Horner's syndrome (sympathetic) or laryngeal paralysis (RLN).
IV. EPAXIAL (Dorsal) MUSCLES:
• Longissimus capitis, Splenius, Semispinalis capitis — extend head/neck.
• Rhomboideus — moves scapula.
V. HYPAXIAL (Ventral) MUSCLES:
• Longus capitis, Longus colli, Scalenus — flex head/neck.
// COMPARATIVE ANALYSIS
| HORSE |
Jugular furrow well-defined. Avoid lower 1/3 — carotid lies just under jugular vein → risk of arterial puncture. |
| CATTLE |
Jugular furrow shallow because of heavy brisket; venepuncture in upper 2/3. |
| DOG |
Cervical muscles smaller. Jugular vein still palpable for anaesthesia sample. |
CLINICAL RELEVANCE
Jugular Venepuncture: Standard IV in cattle & horse — upper third of furrow. Carotid Hit (Horse): Bright red pulsatile blood — life-threatening if drug injected (PROCAINE → seizures). Horner's Syndrome: Damage to vagosympathetic trunk → ptosis + miosis + enophthalmos + 3rd eyelid prolapse.
