The neural spines of successive dorsal vertebrae in specimens of the Early Permian cotylosaur Captorhinus aguti alternate in height. The pattern of alternation is almost, but apparently not quite, completely regular. The difference in height between successive neural spines is greater in the anterior part of the column, becoming less pronounced posteriorly. This condition occurs also in another captorhinomorph cotylosaur, Captorhinikos sp., and is similar to the pattern recently described in the microsaur Pantylus cordatus by Carroll. Detailed features of the higher spines indicate that this condition was associated with modification of the system of supraspinal and interspinal ligaments and that these ligaments may have acted as posterior extensions of the nuchal ligament, possibly in correlation with a relatively large skull.