It is shown that by means of an X-ray diffractometer that in bone diaphyses of dog (Canis familiaris L.), wolf (Canis lupus L.), ox (Bos taurus L.), aurochs (Bos primigenius Boj.), domestic pig (Sus domesticus L.), and wild boar (Sus scrofa L.), the hydroxyapatite crystals are in all probability oriented with the basal pinacoid (002) at right angles to the long axes of the bones, although in some areas of the distal epihyses they parallel the long axes of the bones. No difference is found in the orientation of the crystals either between domestic and wild animals or between carnivores, ruminants and omnivores.