Transverse Rotation of the Thoracolumnbar Spine
A 7 year child old can remember all the names of the pokemon creatures. I can not, but you can remember transverse rotation of the thoracolumnbar spine. I'll help by repeating it often.
"Transverse" indicates the direction of the rotation. Think of the hands of a clock. If you are facing the clock, the hands rotate left or right on an arc around the pin that attaches them. The wall the clock is attached to represents the transverse plane as long as you are facing it. (Plane refers to an imaginary two dimensional surface for referenc purposes). From the saddle transverse rotation of the thoracic spine is like the hand of the clock, but obviously the freedom of movement is much less. When looking from behind the horse, when the withers (part of the thoracolumnbar spine) are at 12 o'clock it is vertical. If it is at 11:57 with right bend, this is called inverted transverse rotation. 11:57 with left bend is correct transverse rotation and this is the healthy kinematic.
"Rotation" is a word you know.
"Thoracolumnbar Spine:" it's a column, it's part of the thorax, the thorax is the part of the creature that is enclosed by ribs. It is the same as the Thoracic Spine. "Thora" is your clue. Transverse Rotation of the Thoracic Spine occurs between T9 and T14 (the 9th and 14th thoracic vertebrae.) This is how bending is created. Bending occurs between T9 and T16. On the horse, this is where the rider sits.