The study of these plates seems to show that the sacra and sacro-iliacs may be divided into three types. Type 1 is seen in both males and female.

Type II is distinctly a male type and Type III distinctly female.

In Types I and II, over-lapping transverse processes are common. It is impossible to tell, however, from the X-ray whether this is merely an overlapping of the shadows or whether there is actual contact. It seems probable that where contact takes place, it is more likely to occur in Type II. Type II also seems to show more irregularities in the shape of the transverse processes, and in the structure of the sacrum and shape of the sacro-iliacs.

The measurements, not of great accuracy for comparative use owing to the varying conditions, but constant in each case, seemed to show a very definite and, in many cases, a marked asymmetry.

The size and shape of the transverse processes varied greatly and in the majority of cases were quite asymmetrical, of distinctly different types. Even in those cases where they were alike they showed distinct differences, and in a large number of cases they pointed upward to a greater or less extent.

Large fan-shaped transverse processes are rather common; when single they seemed to occur more frequently on the left side. They are much more common in the second type.

Bifurcation of the first sacral spinous process is fairly frequent, 6% of the cases showing this defect.

Spondylolisthesis of varying degree is probably more common than usually supposed, also rotation and slipping between the lumbar and sacral articulations.

There are also rarer cases that show congenital malformations.

In conclusion, there seems to be no one type that might be called normal. There are many variations in the lumbo-sacral region. Asymmetry is the predominating feature, and, at any rate from the X-ray, it is impossible to say which special combination of types is normal.