part of part of dorsum withers The ridge between the shoulder blades of a four-legged mammal. Wikipedia:Withers SCTID:89778005 The withers in horses are formed by the dorsal spinal processes of roughly the 3rd through 11th thoracic vertebrae (most horses have 18 thoracic vertebrae), which are unusually long in this area. The processes at the withers can be more than 12 inches (30 cm) long. UBERON:0017749 external soft tissue zone