The influence of experimental deformation on neurocranial Wormian bones in rats

Two hundred and twenty crania of Wistar rats were experimentally deformed. The growth of the anterior vault was restricted in one subgroup and the growth of the posterior vault was restricted in the second subgroup. Seventy‐seven deformed animals survived up to the thirtieth day of age and were sacrificed. Both subgroups were compared with each other as well as with 37 surviving sham‐operated animals and 51 controls, all samples being 30 days of age (group A). Additionally, 33 normal crania of animals sacrificed at 1, 10 and 20 days as well as 19 deformed crania of 10 and 20 days old were observed (group B). Chi‐square and Z tests were employed. Wormian bones found in the skulls of normal growing rats apparently represent an epigenetic polymorphism. Higher frequencies of wormian bones were found in deformed crania than in sham‐operated ones and controls. Experimental deformation may be an extra‐genetic factor that affects the normal genetic expression of wormian bones. This concept is relevant to studies of human population differences based on discontinuous cranial traits.