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76 DESIGN IN NATURE<br />
PLATE XLVII<br />
Plate xlvii. illustrates the longitudinal and transverse cleavages or segmentation of the body and limbs in<br />
vertebrates. The longitudinal, with a certain amount of transverse, cleavage is well seen in the limbs ; the trans-<br />
verse cleavage being marked in the vertebral column and ribs. This plate also illustrates division and radiation,<br />
seen more particularly in the hands and feet or their representatives, namely the fins, flippers, and swimming tails<br />
of fishes and sea mammals, and the diving, swimming, and flying wings of birds. It further shows that the<br />
extremities and other parts of the body are spirally constructed. (Compare with Plates xlv., xlvi., xlviii., and xUx.)<br />
Pig. 1.—Skeleton of golden eagle (Aquila chrysaetos), Scotland. Specially drawn for the present work from specimen in the<br />
British Mnseuni, by C. Berjeau. a, Shoulder joint; b, humerus ; c, elbow joint ; d, e, bones of fore-arm ; /, carpus and wrist joint;<br />
g, thumb or false wing ; h, i,j, k, I, m, a, bones of the hand more or less fused together. This part of the wing bears the primary<br />
or flying feathers, where division and radiation are carried to an extreme, o, Hip joint; ^, femur ; q, knee joint; r, bones of leg;<br />
s, ankle joint ; t, u, tarsus ; v, foot. It will be observed that the wings are powerful structures as compared with the legs and other<br />
parts of the body. This is necessary for the purposes of flight. The modifications of the hands are at once striking and remarkable.<br />
Compare with the hand of extinct flying reptile {Scopognalhus cramrostris), Fig. 2, and the hand of man (Homo sapiens), Fig. 3 of<br />
this Plate.<br />
Fig. 2.—Skeleton of arm, fore-arm, and hand of extinct flying reptile {Scopognalhus crassirostris), Nicholson and Lydeker. Shows<br />
longitudinal and transverse cleavage and extreme modification of the fifth digit (v.) to carrying a flying membrane, h, Humerus ;<br />
r, u, radius and ulna (bones of fore-arm); c, carpus or wrist joint; ii., iii., iv., v., bones of hand; the fifth digit (v.) being very<br />
greatly enlarged for the purposes of flight.<br />
Fig. 3.—Bones of human arm, fore-arm and hand. Shows longitudinal and transverse cleavage, and how all the bones are twisted<br />
upon themselves and form spiral structures.<br />
A. Entire arm. The humerus is twisted upon itself, as indicated by the darts a, b, c, d. The same is true of the radius and ulna<br />
(vide darts ef, gh), and the bones of the hand.<br />
B. Another view of humerus, showing marked spirality.<br />
C. Shows spiral structure of radius.<br />
D. Shows spiral structure of ulna.<br />
The bones of the wing of the bird and even the primary feathers are twisted upon themselves to form spiral structures. The<br />
bones of the human leg and those of birds and quadrupeds are also spirally formed. Compare with extremities of elephant (Plate<br />
XX., Fig. 3). Drawn from specimens in the Author's museum^ by C. Berjeau.<br />
Fig. 4.—Hind flipper of extinct Ichthyosaurus or fish reptile (Ichthyosaurus tenuirostris), (after Owen), with portion of skin and soft<br />
parts adhering. Shows longitudinal and transverse division and segmentation of a marked kind, a, b, c, Anterior or thick margin<br />
of flipper ; cl, e, f, posterior or thin flexible margin of flipper. The flipper is triangular in shape and graduated, and is a true<br />
swimming organ. It is movable in all its parts, and resembles a flying wing. The flipper is essentially a modified hand. It is seen<br />
in position at Plate xlviii., Fig. 3. Compare with the flippers of the extinct Plesiosaurus in same Plate, Fig. 2, and with the modified<br />
hand of the bird's wing and extinct flying reptile (Figs. 1 and 2 of this Plate).<br />
Fig. 5.—Skeleton of the dugong (Halicore dugong), one of the flsh-like, swimming mammals (after Dallas). Shows well-marked<br />
longitudinal and transverse cleavage of body and limbs. The flipper or swimming arm in this case consists of a scapula (a) ; an arm (b) ;<br />
a fore-arm (c) ; and a hand with five digits (d). The bones are all twisted, and the Hipper is moved spirally so as alternately to seize<br />
and evade the water.<br />
Fig. 6.—Skeleton of common seal (Phoca vitulina), (after Cuvier). Shows longitudinal and transverse cleavage in body and<br />
limbs, especially in the latter. The fore limb consists of a scapula (a) ; a humerus (b) ; radius and ulna (c, d) ; wrist (e) ; and hand with<br />
five digits. It closely resembles that of the dugong (Fig. .5 of this Plate). The hind limb consists of femur (h), attached to pelvis (q) ;<br />
radius and ulna {i,j) ; ankle jomt (k) and foot with Ave toes (I). The movements of the fore limbs are similar to those occurring in<br />
the dugong. The movements of the hind limbs resemble in all respects those made by the lower part of the body and tail of the<br />
fish, 'i'he hind limbs are held together and made to lash from side to side in swimiiiing, the toes of the feet and the membrane<br />
supported by them being alternately spread out and contracted during the swimming movement, as happens also in the caudal fins<br />
of fishes. The contour of the seal, like other sea mammals, is fish-like.<br />
Fig. I.—Spirlfar striahis. Shows radiating and right and left-handed spiral arrangements. Compare with i Plate xiv Fie 1<br />
1 A, B, 0, D.<br />
6- )<br />
PLATE XLVIII<br />
Plate xlviii. illustrates longitudinal, radiating, and transverse cleavage and segmentation in the fins, tail, and<br />
body of the fish ; in the flippers and bodies of the extinct bird-Uke and fish-like reptiles (Plesiosaurus and Ichthyo-<br />
saurus) ;<br />
and in the arms and tentacles of modern and extinct cuttle-fishes.<br />
Fig. L-—Skeleton of perch (Ferca), (after Ouvier and Valanciennes). Shows elliptical-shaped, flattened body, with pointed backbone<br />
furnished with spines and ribs, specially arranged to admit of the sinuous lateral movements necessary in swimming. In these movements<br />
the radiating, branching parts of the tail play a conspicuous part, the radiating, branching fins being engaged m a minor desree<br />
a, a', Dorsal fins ; b, pectoral fin ; c, ventral fin ; d, anal fin ; e, e', caudal fin. The pectoral and anal fins occupy the position's of<br />
the anterior and posterior extremities of the seal and other sea mammals.<br />
Fig. 2.— Skeleton of the great extinct bird-like reptile, Plesiosaurus (Plesiosaurus doUchodeirus, Upper Triassic and Liassic) Cafter<br />
Cuvier). Shows typical longitudinal and transverse segmentation in the four flippers, and pronounced transverse segmentation in tli "<br />
long, graceful, spinal column with its spinous processes and ribs. While the spinal column in this extinct form was flexible as in th''<br />
fish, there can be no doubt that locomotion was effected almost exclusively by the flippers, which are specially modified to act