38 DESIGN IN NATURE 



PLATE XXI 



Plate xxi. illustrates the spiral formation of human bones as seen in the arm, leg, vertebral column, clavicle, 

 scapula, and pelvis. 



Fig. 1.— BuiKis of right upper extremity of man witli hand pronated : also separate buiies. All these bones present iine examples 

 of spiral strurtiues ; pronation of the hand being perl'ormed by the radius twisting round the ulna. 



A. The .spirality or twist in the humerus or arm bone is indicated by the darts a, b, and c, d, and in the radius and ulna 

 by the darts e, f, and y, h. 



B. Another view of the humerus, the darts, as before, indicating the spirality, which is very marked. 



C. Radius (one of the bones of the fore-arm), twisted upon itself. 



D. Ulna (bone of fore-arm), twisted upon itself (see darts). 



E. Different view of ulna. The bones of the lower extremity (femur, tibia, and fibula) are also twisted, and so resemble the 

 upper ones. Compare with the fore limb of the elephant (Plate xx., Fig. 3) and tlie structures mentioned in connection therewith. 



Drawn to scale by C. Berjeau from specimens in the Author's museum. 



Fig. 2. — Bones of right lower extremity of man, with metatarsal bone of foot. All these bones are spiral in their nature; the 

 spiral being particularly well seen on the posterior surface of the femur or thigh bone. 



F. Femur or thigh bone seen posteriorly. The darts i,j, and k, I, indicate the direction of the spirality and how the ridges of the 

 bone tend to cross each other. 



G. Tibia and fibula. In this figure the direction of spirality is indicated by the darts q, r, and s, t. 

 H. Another view of the tiliia; the spirality being indicated by the darts in, ii, and o, p. 



1. Another view of the fibula in which the spirality is well marked. 



Drawn to scale b}- C. Berjeau from specimens in the Author's museum. 



Pie. 3. — The human vei-tebral column or backbone. It consists of a chain of small .square-shaped bones with spines and 

 transverse jirocesses for the attachment of muscles ; the bones lieing held together by ligaments and inter-\'ertebral cartilages, which 

 act as buffers and diffuse shock. The colunm displays four antero-posterior curves ; the convexities of two of which are directed 

 anteriorly and two posteriorly. There is also a certain amount of lateral curving which enables the column to move practically in 

 every direction, namely, from before backwards, from side to side, and spirally round its long axis. The column is at once one of 

 the strongest and most mobile parts of the body ; it is also the most elastic and springy part. It furnishes a perfect structure for 

 neutralising shock, especially vertical shock. 



Figs. 4 and 5. — Illustrate the spiral twisting of the bones in the human clavicle, scapula, and pelvis. These bones, like those of 

 the upper and lower extremities, the ribs, &<■., are all distinctly twisted and spiral in their nature. 



A. Human clavicle spirally twisted and resembling the letter/, tlie true line of beauty and of strength (see darts a, !i, and c, rf). 



B. Human pelvis, on the whole the strongest combination of bones in the body. Its several parts are distinctly spiral, as 

 indicated by the darts c, /, and g, h. 



C. Human scapula seen anteriorly. This bone is strengthened by strong ridges and processes, which distinctly tend to cross each 

 other spiral-fashion (see darts i, j, and k, I), 



D. Human scapula seen posteriorly. The same spiral twisted arrangement seen in C is repeated (see darts m, », and o, p). 



Drawn to scale by C. Berjeau from specimens in the Author's museum. 



§ 8. Examples of Radiating and Concentric Arrangements in Plants and Animals, as illustrating 

 Symmetry of Form. 



I have directed attention to the radiating and concentric arrangements which obtain in crystals, in plants, 

 and in animals, and the subject, it appears to me, is so important, from a fundamental point of view, that I will be 

 excused if I devote a little more time to its elucidation and illustration. On the radiating and concentric arrange- 

 ments very largely depend the symmetry of certain crystals and that of the majority of plants and animals. 

 Symmetry, where radiating and concentric arrangements prevail, is more or less assured. It is otherwise in the 

 case of spirals. Single spiral structures are always unsymmetrical, and in order to secure symmetry the spiral must 

 be divided into two (or more) portions ; the portions being made to start from corresponding opposite points above 

 and below or from the sides, and made to wind into each other. While spiral symmetrical structures must consist 

 of at least two parts, they may consist of four, eight, or multiples of these. Symmetry is also produced when right 

 and left-handed spirals are superimposed and made to cross each other. 



The radiating and concentric arrangements receive their most striking illustrations in transverse sections of 

 plants and trees, but they are seen everywhere ; in crystals, and in plants and animals, and parts thereof. The 

 sections of hail seen at Fig. 2, p. 2, and the sections of animal structures depicted at Plate v., p. 9, are very 

 illustrative. In order, however, to save the reader the trouble of comparison I append additional examples of 

 these arrangements [vide Plates xxii. to lii. inclusive). 



The radiating and concentric arrangements are seen in sections of the stems, branches, and roots of plants and 

 trees ; in the arrangements of flowers and fruit ; in the arrangements of spores, zooids, and corals ; in the arrange- 

 ments of shells, scales of fishes, horns, hoofs, and claws ; in the arrangements of muscles, nerves, bones, teeth, &c. 

 In plants, trees, shells, scales, &c., the concentric arrangements, for the most part, indicate layers of groAvth. 



The following illustrations (Plates xxii. to xxviii. inclusive) will explain themselves. 



