Iowa State University Veterinarian Records, RS 22/6/0/9, University Archives, Special Collections Department, Iowa State University, http://www.add.lib.iastate.edu/spcl/arch/rgrp/22-6-0-9.html
A two-year-old American Saddle horse was admitted to the clinic on June 4, 1953, with the following history. During the process of halter breaking, the horse reared up in the stall, broke the halter rope and fell over backwards, striking its head on the cement floor. The following day a swelling was noticed on the back of the head, and the local veterinarian was called. He applied hot packs and later opened the area and removed a small piece of bone. However, abscess drainage continued and the patient was referred to the college clinic showing a fistula in the poll region much like that seen in poll evil.
"Removal of a Sequestrum in a Horse,"
Iowa State University Veterinarian: Vol. 16
, Article 8.
Available at: http://lib.dr.iastate.edu/iowastate_veterinarian/vol16/iss1/8