📝 STANDARD DESCRIPTION:
Two main divisions of skeleton:
• Axial Skeleton — skull, vertebral column, ribs, sternum.
• Appendicular Skeleton — bones of forelimb + hindlimb (girdles + free limbs).
• Visceral Skeleton — bones in soft organs (e.g., os cordis in ox heart, os penis in dog).
• Splanchnic / Heterotopic Skeleton — same idea (bones found outside the typical skeleton).
Classification of bones (by shape):
1. Long bones — femur, humerus.
2. Short bones — carpal, tarsal bones.
3. Flat bones — scapula, skull bones.
4. Irregular bones — vertebrae.
5. Sesamoid bones — patella (largest), proximal/distal sesamoids of fetlock — develop within tendons.
6. Pneumatic bones — air-filled, in birds (humerus, sternum).
📚 DETAILED DESCRIPTION:
SKELETAL ORGANIZATION
I. AXIAL SKELETON — bones along the long axis:
• Skull (cranial + facial bones, hyoid bone).
• Vertebral column — Cervical, Thoracic, Lumbar, Sacral, Coccygeal.
• Ribs + sternum.
• Vertebral formula:
– Ox: C7 T13 L6 S5 Cy18-20
– Horse: C7 T18 L6 S5 Cy15-21
– Dog: C7 T13 L7 S3 Cy20-23
– Pig: C7 T14-15 L6-7 S4 Cy20-23
– Fowl: C13-14 (variable), with synsacrum + pygostyle.
II. APPENDICULAR SKELETON — limbs:
• Forelimb: Pectoral girdle (scapula, clavicle—reduced in domestics) → humerus → radius+ulna → carpus → metacarpus → phalanges.
• Hindlimb: Pelvic girdle (os coxae) → femur → patella + tibia + fibula → tarsus → metatarsus → phalanges.
III. VISCERAL / HETEROTOPIC SKELETON — bones embedded in soft tissues:
• Os cordis in heart of ox/buffalo.
• Os penis in dog, walrus, raccoon.
• Os clitoris in bitch.
• Os rostri in pig snout.
• Os priapi in some carnivores.
• Bacculum (general term for os penis).
BONE SHAPES (Detailed):
• Long bones (Os longum) — clearly longer than wide; have shaft + 2 ends; serve as levers.
• Short bones (Os breve) — cuboidal; carpus, tarsus; dissipate stress.
• Flat bones (Os planum) — broad surfaces for muscle attachment; protective (skull).
• Irregular bones (Os irregulare) — vertebrae, mandible.
• Sesamoid bones (Os sesamoideum) — within a tendon; reduce friction; patella (largest), fabella, distal sesamoid (navicular).
• Pneumatic bones (Os pneumaticum) — air-filled; birds; some skull bones in mammals.
OSTEOLOGICAL TERMS YOU MUST KNOW:
• Foramen — hole.
• Fossa — depression.
• Sulcus — groove.
• Tubercle, Tuberosity, Trochanter, Crest — projections for muscle attachment.
• Condyle — rounded articular projection.
• Process — any bony outgrowth.
• Spine — sharp ridge.
• Facet — small flat articular surface.
• Notch (Incisura) — indentation.
• Sinus — air-filled cavity in a bone.
• Canal — bony tunnel for vessels/nerves.
// COMPARATIVE ANALYSIS
| OX |
Total bones ≈ 207. C7-T13-L6-S5-Cy18-20. |
| HORSE |
Total ≈ 205. T18 — most thoracic vertebrae among large mammals. |
| DOG |
Total ≈ 319 (highly variable due to coccygeal). L7. |
| FOWL |
Many bones fused into compound bones (synsacrum, tarsometatarsus, tibiotarsus). |
CLINICAL RELEVANCE
Vertebral Formula Rule: 'Cattle and Cars share C7 T13 L6' — easy mnemonic. Splanchnic bones become incidental findings on radiographs (e.g., os cordis must not be confused with cardiac calcification).
