This is an amazing set as the skull and the sacrum are both from the same skeleton. There are very strong patterns in both specimens and in these pieces, you see how they reflect each other ("As above, so below". Randolph Stone D.O.). The cranium has both a inferior vertical shear pattern and a lateral shear pattern and there is considerable torsion and side bending as well. This is reflected in the sacrum and you can see the twist and side bend in relationship to the sacral base.
The sacrum is unusual in that it has six segments and a huge medial promontory. The sacral nerve canal is cast all the way through (rather than plugged as on less expensive models), and you are able to see the connections into the sacral segment foramen. There was such a strong bend in the sacrum that the lumbar transverse process was rubbing on the sacral base.
This is an important set for understanding cranial and sacral distortions and how they affect each other.