The cervical rib may be complete, in which it is frequently fused to the first thoracic rib (A), or it may be incomplete with a fibrous band to the first thoracic rib (B). The elongated transverse process of C7 may function similarly to an incomplete cervical rib, but is anatomically distinct from a rib in its continuity with the C7 vertebra (C). ([A] From Makhoul RG, Machleder HI. Developmental anomalies at the thoracic outlet. J Vasc Surg. 1992;16:538; with permission; and [B] From Makhoul RG, Machleder HI. Developmental anomalies at the thoracic outlet. J Vasc Surg. 1992;16:538; with permission; and [C] Courtesy of Dave Klemm, Georgetown University School of Medicine.)