Growth control of the cranial base -- A study with experimentally bipedal female rats

In a cross-sectional study the postnatal development of the skull, particularly that of the cranial base, was studied in experimentally bipedal female rats, up to the age of 46 weeks. A total of 71 bipedal and 86 control female animals were studied. It was found that, as compared with control rats, the bipedal rats initially developed a more spherical skull. This was the result of a stronger dorsal flexion of the cranial base at the spheno-occipital synchondrosis. By the end of the observation period this difference had disappeared. This was due to a continuing flexion of the cranial base in the control rats, while the bipedal rats showed almost no change. As to the chondrocranial elements, the basi-occipital bone attained, on the average, the same length in bipedal rats as in controls. However, the basisphenoid bone was significantly shorter. This could be related to the altered shape of the neurocranium, which is eventually significantly shorter and smaller in the bipedal rats, as well as to a change in shape of the brain. In addition to these extrinsic influences, the condition of experimental bipedia could affect the growth of the cranial base, possibly due to increased use of the snout in many behavioural situations, in the absence of the forelegs.