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During a period extending from January 1930 to June 1942, the Department of Radiology at the University of Colorado Medical School and Hospitals made 38,105 roentgenograms of those portions of the body which lend themselves specifically to a study of rib abnormalities. This includes all roentgenograms of the spine, chest, and abdomen. Among the number there were found 59 rib abnormalities (0.15 per cent of the total). For purposes of simplification, the anomalies have been grouped into seven classifications: (1) cervical ribs; (2) lumbar ribs; (3) bipartition, or “forking” of the anterior end of a rib; (4) synostosis, or bony union of adjoining ribs; (5) “tile-roof” ribs, or imbrication of ribs; (6) rudimentary ribs; (7) other deformities. Cervical Ribs Nineteen instances of cervical ribs, or 32 per cent of the 59 cases, were seen. Details as to their number, length, occurrence unilaterally or bilaterally, and whether they were jointed or non-jointed, are given in Table I. In every instance the cervical r...

EXAMINATION of hundreds of young chicks in making hormone assays revealed that the number of ribs is variable, including deficiencies and additions of portions of ribs. To determine more definitely the nature of these variations, a new series of chicks was examined for this purpose. A total of 522 chicks were examined, 335 of which were Single Comb White Leghorn males and females. The others were crosses of Leghorns and heavy breeds. Of the 522 chicks examined, 89.6 percent were considered normal and 10.4 percent abnormal in rib structure. Chicks from three different hatcheries showed no significant differences in the incidence of abnormalities and there was no difference between males and females. In the usual arrangement, the first two ribs are floating and composed of a single portion each. The next four are articulated to the sternum and each is composed of a dorsal and a ventral portion with a …