We find the same biserial primitive fin more or less preserved in the fossilised remains of the earliest Selachii (Figure 2.248), Ganoids (Figure 2.253), and Dipneusts (Figure 2.256). It is also found in modified form in some of the actual sharks and pikes. But in the majority of the Selachii it has already degenerated to the extent that the radii on one side of the fin-rod have been partly or entirely lost, and are retained only on the other (Figure 2.337). We thus get the uniserial fin, which has been transmitted from the Selachii to the rest of the fishes (Figure 2.338). (FIGURE 2.347. Human skeleton. (Cf. Figure 2.326.) FIGURE 2.348. Skeleton of the giant gorilla. (Cf. Figure 1.209.)) Gegenbaur has shown how the five-toed leg of the Amphibia, that has been inherited by the three classes of Amniotes, was evolved from the uniserial fish-fin.* (* The limb of the four higher classes of Vertebrates is now explained in the sense that the original fin-rod passes along its outer (ulnar or fibular) side, and ends in the fifth toe. It was formerly believed to go along the inner (radial or tibial) side, and end in the first toe, as Figure 2.339 shows.) In the dipneust ancestors of the Amphibia the radii gradually atrophy, and are lost, for the most part, on the other side of the fin-rod as well (the lighter cartilages in Figure 2.338). Only the four lowest radii (shaded in the illustration) are preserved; and these are the four inner toes of the foot (first to fourth). The little or fifth toe is developed from the lower end of the fin-rod. From the middle and upper part of the fin-rod was developed the long stem of the limb--the important radius and ulna (Figure 2.339 r and u) and humerus (h) of the higher Vertebrates. In this way the five-toed foot of the Amphibia, which we first meet in the Carboniferous Stegocephala (Figure 2.260), and which was inherited from them by the reptiles on one side and the mammals on the other, was formed by gradual degeneration and differentiation from the many-toed fish-fin (Figure 2.341). The reduction of the radii to four was accompanied by a further differentiation of the fin-rod, its transverse segmentation into upper and lower halves, and the formation of the zone of the limb, which is composed originally of three limbs before and behind in the higher Vertebrates. The simple arch of the original shoulder-zone divides on each side into an upper (dorsal) piece, the shoulder-blade (scapula), and a lower (ventral) piece; the anterior part of the latter forms the primitive clavicle (procoracoideum), and the posterior part the coracoideum. In the same way the simple arch of the pelvic zone breaks up into an upper (dorsal) piece, the iliac-bone (os ilium), and a lower (ventral) piece; the anterior part of the latter forms the pubic bone (os pubis), and the posterior the ischial bone (os ischii).