📝 STANDARD DESCRIPTION:
Sacrum (Ox):
- 5 sacral vertebrae fused into a single triangular bone.
- Forms the roof of the pelvis.
- Articulates with ilium (sacroiliac joint).
- Sacral foramina (4 dorsal + 4 ventral pairs) for sacral nerves.
- Sacral canal continues spinal canal — site for CAUDAL EPIDURAL.
Coccygeal (Caudal) Vertebrae:
- Number variable: ~18-20 in ox, ~18 in horse, 20-23 in dog, 20-23 in pig.
- First few resemble lumbar; rest become simple rod-like bones.
- Lose spines, transverse processes, and arches caudally.
- Hemal arches/processes on ventral surface of cranial coccygeal vertebrae (Cy3-Cy4 in ox) — protect ventral coccygeal artery (used to feel pulse in cattle).
📚 DETAILED DESCRIPTION:
SACRUM — THE WEDGE BETWEEN THE HIP BONES
The sacrum is a single triangular bone formed by the fusion of 5 sacral vertebrae in ox. It is wedged between the two ilia, transmitting body weight from the spine to the pelvis.
FEATURES:
• Base: Cranial end; articulates with last lumbar vertebra. The cranial border of the body forms the promontory — important landmark for pelvic measurement.
• Apex: Caudal end; joins first coccygeal vertebra.
• Auricular surfaces: Ear-shaped articular surfaces on the sides for the ilium → sacroiliac joint.
• Median sacral crest: Fused spinous processes on top.
• Sacral foramina: 4 pairs of dorsal foramina + 4 pairs of ventral foramina that transmit dorsal and ventral branches of sacral spinal nerves.
• Sacral canal: Continuation of the vertebral canal; contains the caudal end of the spinal cord (cauda equina) and meninges.
COCCYGEAL (CAUDAL/TAIL) VERTEBRAE:
The number varies between species (around 18-20 in ox, slightly more in dog/pig). The first 2-3 are like miniature lumbar vertebrae; the rest become simple cylindrical rods as they go caudally — losing their arches and processes.
HEMAL ARCHES: On the ventral side of the bodies of Cy3-Cy4 (and sometimes more) there are small bony arches (or just hemal processes). They form a tunnel for the ventral median coccygeal artery and vein — used clinically to check pulse and to take blood from cattle (tail bleeding).
EPIDURAL SITE: The space between Sacrum-Coccygeal-1 (S5-Cy1) or between Cy1-Cy2 is the standard site for caudal epidural anaesthesia in cattle. The first movable joint behind the rump is felt when you raise and lower the tail (the 'pump handle' joint).
// COMPARATIVE ANALYSIS
| HORSE |
Sacrum has 5 vertebrae too, but spinous processes are SEPARATE (median crest is interrupted). Coccygeal ~18. |
| DOG |
Sacrum has 3 fused vertebrae only. Coccygeal vertebrae 20-23 (long tail). |
| PIG |
Sacrum 4 vertebrae. Coccygeal ~20-23. |
| FOWL |
Sacrum + last thoracics + lumbars + first coccygeals all fuse into a single bone called the SYNSACRUM. Last 4-6 caudal vertebrae fuse into PYGOSTYLE (supports tail feathers). |
CLINICAL RELEVANCE
Caudal Epidural Anaesthesia (cattle): Local anaesthetic injected into the epidural space at the S5-Cy1 or Cy1-Cy2 junction. Used for: obstetric procedures, vaginal/rectal/perineal surgery, prolapse correction. The injection blocks the last sacral and all coccygeal nerves — anus, vulva and tail become numb but the cow stays standing.
Cranial Epidural: Higher dose at L6-S1 — paralyses the hindlimbs (animal must be cast). Used for major hindlimb/udder surgery.
Tail bleeding (coccygeal venipuncture): Standard route to draw blood from cattle — needle inserted on the ventral midline of tail at Cy3-Cy4 level into the ventral coccygeal vessel.
