Studies on orthocephalization. 8. Behaviour of the visceral part of the rat head in the period between 7 and 60 days after gestation.

The present paper considers the significance of interosseous flexions of the palatal complex in the process of orthocephalization of the rat skull between 7 and 60 d after birth. The study is based on a sample of 25 female rats who have been X-rayed at 7, 14, 30, and 60 d with subsequent analysis of the photographs obtained. During this period the constituents of the bony palate, i.e. the palatine bone, the palatal process of maxilla and the palatal part of premaxilla grow steadily but with decreasing rate of increase with age. The premaxilla grows the most, while the palatal bone grows the least. The angle between the cranial base and the palatal plane decreases, i.e. the rat skull becomes more orthocranial with age. At the same time, the palate becomes more orthopalatal, primarily by an increase in the angle between the palatine bone and maxilla. As the angle between the cranial base and the palatine bone after 14 d increases, i.e. rotates in the opposite direction of the palatal plane, it may be concluded that the process of orthocephalization in this period is caused by the deflexion of the angle between the palatine bone and maxilla, while it before 14 d is caused by a combination of an interosseous deflexion in the palate and an upwards rotation of the palatine bone relative to the cranial base.