The spine
The dog's vertebral formula is 7 cervical, 13 thoracic, 7 lumbar, 3 sacral (fused into the sacrum) and 20-23 caudal. The number is not fixed in all dogs: in a study of 89 dogs, 4.49% had an extra lumbar vertebra or a transitional vertebra.
The bony thorax
Thirteen pairs of ribs: nine sternal, which reach the sternum, and four asternal, whose cartilages join in the costal arch; the last pair is usually floating. The sternum has eight sternebrae, which in the dog and cat remain separate.
A forelimb without a collarbone
In the dog the collarbone is a vestige of about one centimeter, not connected to the skeleton, embedded in the brachiocephalic muscle. The forelimb attaches to the trunk only through muscles and ligaments, not through a bony joint; the serratus ventralis muscle carries the weight of the trunk. When standing, the forelimbs support about 60% of body weight.
The bones: the scapula, the humerus, the radius and ulna (with the olecranon, the point of the elbow), seven carpal bones, the metacarpus, the phalanges. The toes are numbered I-V from the inside outward; toe I is the dewclaw.
The hind limb
The pelvis, formed by the ilium, ischium and pubis, attaches firmly to the sacrum through the sacroiliac joint: unlike the forelimb, the hind limb has a bony connection to the spine. Then come the femur, the patella, the tibia and fibula, seven tarsal bones (the calcaneus forms the point of the hock), the metatarsus and the toes. The hind limbs are the engine of locomotion.
What corresponds in humans
Forelimb: the dog's elbow is our elbow (humerus, radius, ulna; its point is the olecranon), and the carpus is the wrist, with seven small bones in two rows. Hind limb: the knee (stifle) is our knee — femur, tibia, patella — and bends forward; the hock, the “backward” joint lower down, is the ankle, and its point, the calcaneus, is the heel.
The big difference is posture: the dog is digitigrade, it walks on its toes, with the metacarpus and metatarsus raised off the ground — which is why its “heel” sits high, halfway up the limb, and what looks like a long leg from the hock down is, in fact, the paw.
When growth ends
A widespread idea says that growth stops with sexual maturity. Veterinary sources say otherwise: sexual maturity usually begins at 6-9 months (later in large breeds), but growth continues after that. Skeletal maturity is reached at 8-12 months in small and medium breeds and at 10-16 months in large and giant breeds; adult weight at about 9-10 months in small and medium breeds and at about 15 months in large ones.
Until the growth plates close, intense and repetitive exercise (jumping, long runs on asphalt) is something to discuss with your veterinarian; the atlas gives no individual recommendations.