76 



DESIGN IN NATURE 



PLATE XLVII 



Plate xlvii. illustrates the longitudinal and transverse cleavages or segmentation of the body and limbs in 

 vertebrates. The longitudinal, with a certain amount of transverse, cleavage is well seen in the limbs ; the trans- 

 verse cleavage being marked in the vertebral column and ribs. This plate also illustrates division and radiation, 

 seen more particularly in the hands and feet or their representatives, namely the fins, flippers, and swimming tails 

 of fishes and sea mammals, and the diving, swimming, and flying wings of birds. It further shows that the 

 extremities and other parts of the body are spirally constructed. (Compare with Plates xlv., xlvi., xlviii., and xUx.) 



Pig. 1. — Skeleton of golden eagle (Aquila chrysaetos), Scotland. Specially drawn for the present work from specimen in the 

 British Mnseuni, by C. Berjeau. a, Shoulder joint; b, humerus ; c, elbow joint ; d, e, bones of fore-arm ; /, carpus and wrist joint; 

 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 

 or flying feathers, where division and radiation are carried to an extreme, o, Hip joint; ^, femur ; q, knee joint; r, bones of leg; 

 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 

 parts of the body. This is necessary for the purposes of flight. The modifications of the hands are at once striking and remarkable. 

 Compare with the hand of extinct flying reptile {Scopognalhus cramrostris), Fig. 2, and the hand of man (Homo sapiens), Fig. 3 of 

 this Plate. 



Fig. 2. — Skeleton of arm, fore-arm, and hand of extinct flying reptile {Scopognalhus crassirostris), Nicholson and Lydeker. Shows 

 longitudinal and transverse cleavage and extreme modification of the fifth digit (v.) to carrying a flying membrane, h, Humerus ; 

 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 

 greatly enlarged for the purposes of flight. 



Fig. 3. — Bones of human arm, fore-arm and hand. Shows longitudinal and transverse cleavage, and how all the bones are twisted 

 upon themselves and form spiral structures. 



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 

 (vide darts ef, gh), and the bones of the hand. 



B. Another view of humerus, showing marked spirality. 



C. Shows spiral structure of radius. 



D. Shows spiral structure of ulna. 



The bones of the wing of the bird and even the primary feathers are twisted upon themselves to form spiral structures. The 

 bones of the human leg and those of birds and quadrupeds are also spirally formed. Compare with extremities of elephant (Plate 

 XX., Fig. 3). Drawn from specimens in the Author's museum^ by C. Berjeau. 



Fig. 4. — Hind flipper of extinct Ichthyosaurus or fish reptile (Ichthyosaurus tenuirostris), (after Owen), with portion of skin and soft 

 parts adhering. Shows longitudinal and transverse division and segmentation of a marked kind, a, b, c, Anterior or thick margin 

 of flipper ; cl, e, f, posterior or thin flexible margin of flipper. The flipper is triangular in shape and graduated, and is a true 

 swimming organ. It is movable in all its parts, and resembles a flying wing. The flipper is essentially a modified hand. It is seen 

 in position at Plate xlviii., Fig. 3. Compare with the flippers of the extinct Plesiosaurus in same Plate, Fig. 2, and with the modified 

 hand of the bird's wing and extinct flying reptile (Figs. 1 and 2 of this Plate). 



Fig. 5. — Skeleton of the dugong (Halicore dugong), one of the flsh-like, swimming mammals (after Dallas). Shows well-marked 

 longitudinal and transverse cleavage of body and limbs. The flipper or swimming arm in this case consists of a scapula (a) ; an arm (b) ; 

 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 

 and evade the water. 



Fig. 6. — Skeleton of common seal (Phoca vitulina), (after Cuvier). Shows longitudinal and transverse cleavage in body and 

 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 

 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) ; 

 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 

 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 

 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 

 supported by them being alternately spread out and contracted during the swimming movement, as happens also in the caudal fins 

 of fishes. The contour of the seal, like other sea mammals, is fish-like. 



Fig. I.—Spirlfar striahis. Shows radiating and right and left-handed spiral arrangements. Compare with Plate xiv Fie 1 

 A, B, 0, D. i 1 6- ) 



PLATE XLVIII 



Plate xlviii. illustrates longitudinal, radiating, and transverse cleavage and segmentation in the fins, tail, and 

 body of the fish ; in the flippers and bodies of the extinct bird-Uke and fish-like reptiles (Plesiosaurus and Ichthyo- 

 saurus) ; and in the arms and tentacles of modern and extinct cuttle-fishes. 



Fig. L-— Skeleton of perch (Ferca), (after Ouvier and Valanciennes). Shows elliptical-shaped, flattened body, with pointed backbone 

 furnished with spines and ribs, specially arranged to admit of the sinuous lateral movements necessary in swimming. In these move- 

 ments the radiating, branching parts of the tail play a conspicuous part, the radiating, branching fins being engaged m a minor desree 

 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 

 the anterior and posterior extremities of the seal and other sea mammals. 



Fig. 2. — Skeleton of the great extinct bird-like reptile, Plesiosaurus (Plesiosaurus doUchodeirus, Upper Triassic and Liassic) Cafter 

 Cuvier). Shows typical longitudinal and transverse segmentation in the four flippers, and pronounced transverse segmentation in tli " 

 long, graceful, spinal column with its spinous processes and ribs. While the spinal column in this extinct form was flexible as in th'' 

 fish, there can be no doubt that locomotion was effected almost exclusively by the flippers, which are specially modified to act 



