Fig. 24. Section through a portion of the anterior segment at 85 mm (fourth month) (× 192). The immature ciliary processes (Cp) are at a level anterior to the angle. Pigmentation of the inner layer of the marginal sinus (ms) has reached its base. The future iridial portion of the cup (Ir) has an unpigmented cuboidal, basal lamina-lined epithelium (hollow arrow). Nonpigmented cells in the valleys of the primitive processes are columnar (arrowheads) and slanted in the direction of the fibers. These are attached into a basal lamina-like condensation and stretch partially over the gap between ciliary folds and lens. They are the primitive zonula fibers (zf). Arrow points to the fetal origin of the vitreous base. The atrophying capsulopupillary vessels are indicated by the asterisk. Curved arrow points to anlage of ciliary muscle. AC, anterior chamber; cim, major arterial circle; LE, lens epithelium; Sc, sclera.