Craniofacial development of the rat with respect to vestibular orientation.

The vestibular orientation was applied in the present work. Its purpose was to contribute to the knowledge of the craniofacial development of the growing rat. Sagittal cuts were made in 91 crania from Wistar rats (44 males and 47 females) at 8, 15, 30 and 60 days of age. The x and y coordinates of the sagittal points were determined. The sagittal intersection of the vestibular plane was employed as the abscissa and its perpendicular at the mid point of the external semicircular canal (mesovestibion) as the ordinate. Cranial diagrams were constructed in which the length of the sagittal projection of each bone and its angulation with respect to the abscissa were measured. It was confirmed a progressive evolution towards orthocrania due to the bone rotation complexes, which characterized three cranial regions: the anterior region (frontal-ethmiodal-facial complex) with trigonometric rotation; the mid region (parietal-sphenoidal complex) remained stable, and the posterior region (interparietal-occipital complex) with clockwise rotation. Each complex had its own pattern of rotation. The causal factors reside in the differential increment between the functional components: (a) neurocranium-splanchnocranium, (b) neurocranium-cervical column, (c) dorsal neurocranium-basilar neurocranium and (d) dorsal splanchnocranium-basilar splanchnocranium. Its etiology obeys to the functional requirements induced by the adaptation of the modern rodents.