Cervical Ribs. The cervical ribs (Figure 9) are coossified to the centra (Mal-243, Mal-180, Mal-245, Mal-278, Mal-280, and Mal-301) or are isolated fragments (Mal-64, Mal-146, Mal-147, Mal-149, Mal-162, and Mal-187-2). The ribs are nearly parallel to the long axes of the centra. The heads terminate at the anterior limits of their associated centra in proximal cervical vertebrae (Mal-180), but terminate posterior to the anterior ends of their associated centra in medial and distal cervical vertebrae. This is in contrast to “Titanosauridae indet. DGM Series A” where the heads of the ribs extend beyond the anterior ends of their associated centra (Powell 1986, 1987a). The ribs are thin and dorsoventally compressed, relatively broad transversely in their proximal halves, but thin and rounded rods in their distal halves. The shafts of the ribs in the proximal and medial cervical vertebrae extend up to 320 mm beyond the posterior ends of their associated centra, and even extend beyond the ends of the next succeeding centra. In the distal cervical vertebrae, the shafts of the ribs do not extend beyond the centra (Mal-245).
These occur in 0.5-1% of the population. About 10% of these cause compressive symptoms, ranging from nerve compression (eg pain, paresthaesia and muscle wasting along the medial border of the hand) to subclavian artery post stenotic aneurysm. The remainder are aymptomatic, but are occasionally mistaken for a sinister mass lesion on clinical examination.
They may be large or small, single or bilateral, and may articulate with the first rib. If they consist only of a fibrous band they will not be visible on radiographs. They can be confused with hypoplastic first ribs; remember that the 7th cervical transverse processes point downwards, while the first thoracic transverse processes are angled upwards.
Most people will, I suspect, picture a giraffe. Other likely candidates are swans or long-necked dinosaurs or plesiosaurs; many vertebrates have evolved long, relatively flexible necks, the better to reach food that is otherwise out of reach, or is more easily captured with a mobile head on a flexible stalk.
Filed under: divers |