Topography (study of organ relationships):

Digestive System — from mouth to anus. Starts in head, runs through neck (oesophagus), thorax, abdomen, pelvis. Accessory: liver, pancreas, salivary glands.

Respiratory System — nose → nasal cavity → pharynx → larynx → trachea → bronchi → lungs (in thorax).

Urinary System — kidneys (sublumbar, abdomen) → ureters → urinary bladder (pelvic floor) → urethra (pelvic + penile in male, short in female).

Endocrine System — pituitary (brain), thyroid + parathyroid (neck), adrenals (kidneys), pancreas (islets), gonads.

Male Reproductive — testes (scrotum) + epididymis + ductus deferens + accessory glands (pelvic) + penis.

Female Reproductive — ovaries + uterine tubes + uterus (abdominal/pelvic) + cervix + vagina + vulva.

Avian (Fowl) variations: 1 left ovary, single oviduct, cloaca (common opening).

BIRD'S-EYE VIEW OF THE VISCERAL SYSTEMS

This entry summarises topography only — detailed morphology of each system is covered under the regional modules.

1. DIGESTIVE SYSTEM:
• Head: Oral cavity, tongue, teeth, dental pad (ruminants), salivary glands (parotid, mandibular, sublingual).
• Neck: Oesophagus (cervical part), pharynx, larynx (shared respiratory).
• Thorax: Oesophagus (thoracic part) — passes through diaphragm.
• Abdomen: Stomach (4 compartments in ruminants, 1 in monogastrics), small intestine (duodenum/jejunum/ileum), large intestine (cecum/spiral colon/transverse/descending), liver, pancreas, spleen.
• Pelvis: Rectum, anus.
• Fowl: Crop (food storage), proventriculus (true glandular stomach), ventriculus/gizzard (muscular stomach), short small intestine, paired ceca, cloaca.

2. RESPIRATORY SYSTEM:
• Conducting zone: Nostrils → nasal cavity (olfactory + respiratory regions, paranasal sinuses) → pharynx → larynx → trachea → primary bronchi.
• Respiratory zone: Bronchi → bronchioles → alveolar ducts → alveoli (gas exchange).
• Bovine specialty: Tracheal bronchus (extra bronchus from trachea to right cranial lobe).
• Equine specialty: Guttural pouches (auditory tube diverticula).
• Avian specialty: Air sacs (8-9 pairs) + parabronchi + flow-through ventilation. No diaphragm.

3. URINARY SYSTEM:
• Kidneys (paired, retroperitoneal, sublumbar) → ureters → urinary bladder (pelvic floor) → urethra → external urethral orifice.
• Bovine kidney = lobulated, multipyramidal, no renal pelvis.
• Equine kidney = smooth, bean-shaped (right) / heart-shaped (left).
• Female urethra short; opens in vestibule. Male urethra long, with sigmoid flexure in ruminants.
• Fowl: 3-lobed kidneys; NO bladder; ureters open into urodeum of cloaca.

4. ENDOCRINE GLANDS (locations):
• Pituitary (Hypophysis) — sella turcica of basisphenoid bone, brain.
• Pineal — epithalamus, brain.
• Thyroid — bilateral, on trachea below larynx.
• Parathyroid — internal & external; near thyroid.
• Thymus — cranial mediastinum (large in young, atrophies with age).
• Adrenal — paired, on cranial pole of each kidney.
• Pancreatic islets — within pancreas.
• Gonads (testis/ovary) — produce sex steroids.

5. MALE REPRODUCTIVE SYSTEM:
• Testes (scrotum) → epididymis → ductus deferens → through inguinal canal → ejaculatory duct + accessory glands (vesicular, prostate, bulbourethral) → urethra → penis (fibroelastic in bull/ram/boar with sigmoid flexure; musculocavernous in horse/dog).
• Spermatic cord = pampiniform plexus + testicular vessels + ductus deferens + cremaster muscle, all wrapped in tunica vaginalis.
• Fowl: Internal testes (no scrotum), ductus deferens opens into cloaca; no penis (except duck/goose/ostrich).

6. FEMALE REPRODUCTIVE SYSTEM:
• Ovary → infundibulum → uterine tube (oviduct: ampulla + isthmus) → uterus (bicornuate in ruminants, bipartite in mare, bicornuate-with-long-horns in bitch & sow) → cervix → vagina → vestibule (with suburethral diverticulum in cow) → vulva.
• Suspension: broad ligament (mesovarium + mesosalpinx + mesometrium).
• Fowl: Only LEFT ovary + oviduct functional (right regresses); oviduct = infundibulum, magnum (albumen), isthmus (membranes), uterus/shell gland, vagina; opens into cloaca (urodeum).