. Biology of the vertebrates : a comparative study of man and his animal allies. Vertebrates; Vertebrates -- Anatomy; Anatomy, Comparative. 6o6 Biology of the Vertebratec median fins extend into the body to come in contact with the vertebral column with which they articulate permanently. The basalia of the paired fins, in the absence of other hard skeletal parts in the ventral region of the body, undergo further modification. The most anterior basal enlarges and extends into the ventral body wall until it meets the corresponding part of the opposite side with which it fuses. As a result of the
. Biology of the vertebrates : a comparative study of man and his animal allies. Vertebrates; Vertebrates -- Anatomy; Anatomy, Comparative. 6o6 Biology of the Vertebratec median fins extend into the body to come in contact with the vertebral column with which they articulate permanently. The basalia of the paired fins, in the absence of other hard skeletal parts in the ventral region of the body, undergo further modification. The most anterior basal enlarges and extends into the ventral body wall until it meets the corresponding part of the opposite side with which it fuses. As a result of the union of these two basals a transverse bar, a primitive girdle, is laid down (Fig. 527). Pelvic Girdle. __- Basipterygium -^ Muscle Bud 23 Radial 11 Fig. 528. Pelvic fin of a Scyllium embryo slightly older than that shown in Figure 526. Muscle-buds overlying radials are shown in out- line except over radial 11. (After Goodrich.) 5. Homology and Adaptation The paired appendages of vertebrates above the fishes are all built on the same plan, that is, of the same sequence of bones. This consists typically of a tripod of bones known as the girdle, which is intermediate between the appendage and the backbone; a large shaftlike bone, called either the humerus or femur, according to whether it occurs in the anterior or the posterior pair of appendages; two long bones side by side, the radius and ulna, or the tibia and fibula respectively; a complex of several small bones, making the wrist or ankle; a set of five long slender bones, forming the palm or the sole; and lastly, at the tip of each of the palm or sole bones, two, three, or more small cylindrical bones, placed end to end, known as the digits or phalanges. For a diagrammatic representation of this sequence of bones in the appendages of a land vertebrate, see Figure 529. The principal joints or landmarks of the locomotor skeleton in man are indicated in Figure 530. Each bone of any appendage has its counterpart not only in the
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