Overview
The horse has between fifteen and twenty-one caudal vertebrae (vertebrae caudales), about eighteen being the usual number. They form the skeleton of the dock, the fleshy part of the tail from which the long tail hairs grow. The first ones keep the features of a typical vertebra; towards the tip they lose the arch and the processes and are reduced to ever smaller cylindrical bodies.
Key features
- First caudal vertebrae: have a complete vertebral arch, a low spinous process and broad, flattened transverse processes. The first may fuse with the sacrum in old horses.
- Vertebral canal: narrows quickly; the spinal cord ends within the sacrum, so only the initial part of the cauda equina nerves and the filum terminale pass through the caudal vertebrae.
- Distal caudal vertebrae: body only, no arch.
- Vessels: the median caudal artery runs along the ventral surface of the bodies, between the tail muscles.
Clinical relevance
- Caudal epidural anaesthesia: injected into the space between Cd1 and Cd2 (sometimes between the sacrum and Cd1), found by moving the tail up and down to feel the first mobile joint. It desensitises the tail, perineum and vulva or anus for procedures in the standing horse.
- Tail pulse: the median caudal artery is palpable on the ventral surface of the tail base.
- Tail injuries: fractures or luxations from pulling, falls or knocks against the wall; loss of tail tone accompanies injuries to the caudal and sacral nerves.