Their intersections with the ribs form nodules .
The spaces between the ribs are marked by spiral cords a little less strong than the ribs ; four of these occur between the sutures on the second and third , and seven upon the penultimate turn .
four 's intersections with the ribs form nodules .
The spaces between the ribs are marked by spiral cords a little less strong than the ribs ; four of these occur between the sutures on the second and third , and seven upon the penultimate turn .