Anatomical Variations of the Spine in the Horse

Abstract

The vertebral counts of the thoracic, lumbar and sacral spines of 190 horses and of the sacral and lumbar spines of 256 horses and classified into 9 species are given and the variations are shown. The cervical spine always had 7 vertebrae. While 18 is the usual number of thoracic vertebrae, 17 were found in 18 and 19 in 11 of 190 specimens. Nineteen thoracic vertebrae were found in only 11 of the specimens but of these 11 instances, 9 occurred among 32 spines of the Prjevalsky horse. The domestic horse, Shetland pony, zebras, Arabian horses and hybrids normally have 6 lumbar vertebrae, the donkeys and hemiones have 5 but exceptions were found in all classes. The Prjevalsky horse has 5, or 6 equally divided. It may be proper to think of the Prjevalsky horse as having normally 6 lumbar vertebrae with a high incidence of dorsalization of L1. The sacra usually have 5 vertebrae, this number having been counted 176 times, but 4 vertebrae were counted 49 times and 6 vertebrae 9 times. Caudal vertebrae are often fused with the sacrum making a single functional unit. If such fused caudal vertebrae and transitional sacro-caudal vertebrae are counted as parts of the sacra, of 52 horses with 5 lumbar vertebrae, 2 had 4, 30 had 5, 16 had 6 and 4 had 7 sacral segments; of 180 horses with 6 lumbar vertebrae, 18 had 4, 110 had 5, 44 had 6 and 8 had 7 sacral segments. Horses with 5 lumbar vertebrae had longer sacra, average 5.41, than horses with 6 lumbar vertebrae, average 5.23. The shortest sacra were found in Shetland ponies, horses, Arabians and Prjevalsky horses. The longest sacra were found in Grevy zebras, zebras, donkeys and hemiones. Variation in one portion of the spine results in compensating changes in the neighboring areas.