Larynx = voice box; controls airflow + protects airway during swallowing.
Laryngeal cartilages: Four types are recognized — unpaired epiglottic, thyroid and cricoid cartilages plus paired arytenoid cartilages (five individual pieces). Corniculate and cuneiform structures are processes associated with the arytenoid and epiglottic cartilages, not two additional primary cartilages.
Vocal folds stretched between thyroid + arytenoid cartilages.
Innervation: Recurrent laryngeal nerve (CN X) — except cricothyroideus = cranial laryngeal.

Trachea: Cartilaginous tube; in ox ~50 incomplete C-rings; runs in mid-line of neck. Tracheotomy site = mid-cervical region between 3rd & 5th tracheal rings.

Oesophagus: Muscular tube; in cattle it deviates to the left of the trachea in the cervical region and returns toward the median plane caudally. It has cervical, thoracic and short abdominal parts and passes through the oesophageal hiatus.

LARYNX, TRACHEA & OESOPHAGUS

I. LARYNX (Box of Voice):
Located at the entrance of the lower respiratory tract, in the throat. Functions: airway, voice production (phonation), protection of airway during swallowing (cough reflex).

Cartilages of the Larynx (Ox = 5; Horse = up to 7):
• Thyroid cartilage — largest; shield-shaped; forms ventral & lateral walls; in male horse forms 'laryngeal prominence'.
• Cricoid cartilage — only complete ring of larynx; signet-ring shape (broad part dorsal).
• Arytenoid cartilages (paired) — pyramid-shaped; carry vocal processes; key for vocal fold movement.
• Epiglottis — leaf-shaped; covers entrance to larynx during swallowing.
• Corniculate + Cuneiform cartilages (in horse) — small accessory.

Laryngeal Cavity Subdivisions:
• Vestibule (above vocal folds) — entry from pharynx.
• Glottis (rima glottidis) — narrow space between vocal folds.
• Infraglottic cavity — below vocal folds, continuous with trachea.

Innervation:
• Cranial laryngeal nerve (CN X) — sensory + motor to cricothyroideus.
• Recurrent laryngeal nerve (CN X) — motor to all OTHER intrinsic laryngeal muscles + sensory below vocal folds.
Damage or degeneration of the recurrent/caudal laryngeal innervation can cause laryngeal hemiplegia ('roaring'). Equine recurrent laryngeal neuropathy is predominantly left-sided and multifactorial; the longer left recurrent course is an anatomical association, not a complete causal explanation.

II. TRACHEA:
Tube carrying air from larynx to bronchi. Walls = ~50 incomplete cartilage C-rings (open dorsally, closed by tracheal muscle), connected by annular ligaments.
• Lined by ciliated pseudostratified columnar epithelium with goblet cells (mucociliary clearance).
• Course: cervical (ventral, near the midline) → thoracic (mediastinum) → bifurcation at the carina; vertebral level varies with species and position.
• Ruminant + porcine feature: Tracheal bronchus — a bronchus arising proximal to the bifurcation and supplying the right cranial lung lobe.
• Tracheotomy / Tracheostomy: Mid-cervical region, ventral midline, between 3rd and 5th tracheal rings — emergency airway.

III. OESOPHAGUS:
Muscular tube from pharynx to stomach. Begins dorsal to larynx, descends initially DORSAL to trachea, then crosses to the LEFT side of trachea in the neck, returns to mid-line in the thorax (above heart), pierces the diaphragm at the oesophageal hiatus.
• Wall layers: Mucosa (stratified squamous epithelium) + submucosa + tunica muscularis (skeletal muscle in cervical part — voluntary; smooth muscle in thoracic part of horse but SKELETAL throughout in ox/dog) + adventitia/serosa.
• Esophagotomy: Surgery to remove choke (foreign body); cervical region, ventral or lateral approach.
• Choke: Bolus stuck in cervical oesophagus — common in cattle (potatoes, apples) and horse (pelleted feed).