📝 STANDARD DESCRIPTION:
Splanchnology = study of viscera (Greek splankhna = entrails).
Body cavities (closed sacs containing viscera):
1. Thoracic Cavity:
• Roof: thoracic vertebrae.
• Floor: sternum.
• Walls: 13 pairs of ribs (ox).
• Cranial: 1st rib (thoracic inlet).
• Caudal: diaphragm.
• Contains: heart, lungs, oesophagus, trachea, thymus.
2. Abdominal Cavity:
• Roof: lumbar vertebrae + sublumbar muscles.
• Floor + side walls: abdominal muscles.
• Cranial: diaphragm.
• Caudal: pelvic inlet.
• Contains: stomach, liver, spleen, intestines, kidneys, etc.
3. Pelvic Cavity:
• Roof: sacrum + 1st coccygeal vertebrae.
• Floor: pubis + ischium.
• Walls: ilium + sacrosciatic ligament.
• Cranial: pelvic inlet.
• Caudal: pelvic outlet.
• Contains: rectum, urinary bladder, reproductive organs.
📚 DETAILED DESCRIPTION:
BODY CAVITIES — TOPOGRAPHIC OVERVIEW
The trunk of the animal is divided into three large coelomic cavities lined by serous membranes. Each contains specific viscera (organs).
1. THORACIC CAVITY (Cavum thoracis):
• Boundaries: Roof = thoracic vertebrae; Floor = sternum; Walls = ribs + intercostal muscles; Cranial limit = thoracic inlet (1st thoracic vertebra + 1st rib + manubrium of sternum); Caudal limit = diaphragm.
• Lining: Parietal pleura (lateral & costal pleura against ribs, mediastinal pleura on midline, diaphragmatic pleura on diaphragm).
• Contents: Heart (in middle mediastinum, in pericardial sac), lungs (in pleural cavities), trachea, oesophagus, thymus (young animal), large vessels (aorta, vena cavae, azygos), thoracic duct, lymph nodes, sympathetic chain.
2. ABDOMINAL CAVITY (Cavum abdominis):
• Boundaries: Roof = lumbar vertebrae + sublumbar muscles (psoas major/minor, iliacus); Floor + lateral walls = abdominal muscles + last few ribs; Cranial limit = diaphragm (dome bulges into thorax); Caudal limit = pelvic inlet.
• Lining: Parietal peritoneum.
• Contents: Stomach (4 compartments in ruminants), small + large intestines, liver, gall bladder (absent in horse), pancreas, spleen, kidneys, ureters, adrenal glands, abdominal aorta, caudal vena cava, portal vein.
• Topographic divisions for clinical use:
– Epigastric region (cranial): liver, stomach, pancreas, spleen.
– Mesogastric region (middle): jejunum, ileum, colon, kidneys.
– Hypogastric region (caudal): caudal jejunum, descending colon.
• Paralumbar fossa (Flank) = depression between last rib + tuber coxae + lumbar transverse processes — surgical window.
3. PELVIC CAVITY (Cavum pelvis):
• Boundaries: Roof = sacrum + first 1-2 coccygeal vertebrae; Floor = pubis + ischium (pelvic symphysis); Lateral walls = shafts of ilium + sacrosciatic ligaments; Cranial limit = pelvic inlet; Caudal limit = pelvic outlet (closed by pelvic diaphragm).
• Lining: Cranially peritoneum (continuous with abdominal); caudally retroperitoneal.
• Contents: Rectum, urinary bladder + pelvic urethra, accessory sex glands (male), uterus + cervix + vagina (female); vessels = internal iliacs.
SEROUS MEMBRANES — common architecture:
• Parietal layer lines the body wall.
• Visceral layer covers the organ.
• Between them: small amount of serous fluid → frictionless gliding during organ movement.
• Pleura (around lungs), Pericardium (around heart), Peritoneum (around abdominal viscera), Tunica vaginalis (around testis).
// COMPARATIVE ANALYSIS
| OX |
Massive abdomen because of the rumen complex. Right paralumbar fossa = surgical access (rumenotomy). |
| HORSE |
Long abdomen but smaller GI relative to size. Pelvic cavity proportionally large for foaling. |
| DOG |
Abdomen flexes with spine — agility advantage but disc-disease risk. |
CLINICAL RELEVANCE
Paracentesis Thoracis: Pleural tap at 6th-8th ICS lower third. Abdominocentesis: Right of midline, caudal to xiphoid. Cystocentesis: Bladder tap on ventral midline. Laparotomy approaches: ventral midline, paramedian, or right/left paralumbar fossa.
