1. and further reading COLLES, C. M. & COOK W. R. (1983) Veterintary Record 113, 483
2. Veterinary;COOK, W.R.;Record,1968
3. COOK, W. R. (1973) Journal of the American Veterintary Radiological Society
4. Veterinary;GREET, T.R.C.;Record; Practice; Veterinary Record 114,1981