Fig. 8-10. A, The basic arrangement of the segmental innervation (dermatomes) of the skin of the upper limb, which is supplied successively down the pre-axial border and then up the postaxial border. B, An embryo of 7 weeks (measuring 17 mm between small arrows), showing the longitudinal axes (A) of the upper and lower limbs. The parts of the limbs rostral to the axes are called pre-axial, those caudal to the axes are termed postaxial. The sequence of dermatomes from pre-axial to postaxial is shown on each limb. Cf. fig. 15-11. Click for high resolution image.