This may be of use
Am J Vet Res. 1997 Oct;58(10):1083-91.  

Developmental variation in lumbosacropelvic anatomy of thoroughbred racehorses.

Haussler KK, Stover SM, Willits NH.
Abstract on
This e-mail, and any attachment, is confidential. If you have received
it in error, please delete it from your system, do not use or disclose
the information in any way, and notify me immediately. The contents of
this message may contain personal views which are not the views of the
Company, unless specifically stated. You should not copy, forward or
otherwise disclose the contents of this e-mail or any of its attachments
without express consent