Studies on orthocephalization. 6. Flexions of the rat head in the period between 1 day before gestation and 14 days after gestation.

The present paper considers the significance of a variety of cranial flexions in the process of orthocephalization of the rat skull between 1 day before birth to 14 days after birth. The study is based on a sample of 95 albino rats divided into 5 age groups (1 day before birth - 0 days - 4 days - 7 days - 14 days after birth), who have been sacrificed and x-rayed with subsequent analysis of the photos obtained. Before x-raying, the rat heads have been treated with AgNO3 to improve the contrast of the bone images on the x-ray photos. In the period studied, the angle between the cranial base and the facial part of the skull becomes considerably more obtuse, i.e. the skull becomes considerably more orthocranial. As compared to the changes that have been shown in 14...60 days old rats, the changes in the early period are much more marked. The cranial vault in the young rats studied, also becomes flatter and more square, due to changes between the individual bones of the vault. This flattening is a significant part of the straightening of the rat skull as a whole, i.e. of the process of orthocephalization. In 14...60 days old rats the simultaneous size increase which primarily takes place in the bones of the facial skull reinforces an impression of marked orthocephalization. In the young rats of the present study, the size increase takes place both in the facial and in the cerebral part of the skull. The result of this leaves an impression of only moderate angular changes, although the changes are much more pronounced than in the older rats.