Picture - Cosmic Polymath

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
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.
the radius and ulna
C. Radius (one of the bones of the fore-arm), twisted upon itself.
D.
E.
Ulna (bone of fore-arm), twisted upon itself (see darts).
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, &