Figure 18c. (a, b) Sagittal T1-weighted MR image (a) and corresponding anatomic slice (b) obtained at the PIP joint show the insertion of the central slip (arrow) on the base of the middle phalanx. (c) Axial T1-weighted MR image obtained at the head of the proximal phalanx shows the relationship between the central slip (arrow) and the medial and lateral slips (arrowheads).