The most recent contribution to the little-studied subject of accessory sacro-iliac articulations is that by Mildred Trotter ('37). Her paper, in addition to giving information as to the frequency of the anomaly in another racial group (American Negroes), verifies most of the findings of earlier investigators, especially those of Seligmann ('35).
The present information regarding accessory sacro-iliac articulations in man-the only primate heretofore studiedthus may be summarized briefly from Trotter's paper: Located as a rule just lateral to the first or second (or both) posterior sacral foramen, on one or both sides, accessory facets are found in varying percentages of Whites (10.4, Derry; 50.5, Trotter) depending upon age and sample; they are more common in males than females and tend to increase with age. Trotter's American Negro sample (473) gave an incidence of 20.7 ; KaibG's Mongolians (50) gave an incidence of only 10%. There appears to be no correlation with the presence or absence of other anomalies.
One looks in vain in Trotter's paper for an explanation of these accessory articulations. However, since her findings merely supported those of previous investigators, apparently she was not in a position to offer a new explanation. It is this phase of the subject that I wish to stress in the present paper.