744 A PARENTHETIC NOTE [ch. 



the band to the form of the surface, in "stretching it tight," or in 

 other words in causing it to assume a. direction which is the shortest 

 possible hne upon the surface between the two extremes: and it is 

 only then that further contraction will have the effect of constricting 

 the tube and so exercising pressure on its contents. Thus the 

 muscular fibres, as they wind over the curved surface of an organ, 

 arrange themselves automatically in geodesic curves: in precisely 

 the same manner as we also automatically construct complex 

 systems of geodesies whenever we wind a ball of wool or a spindle 

 of tow, or when the skilful surgeon bandages a Hmb ; indeed the 

 surgeon must fold and crease his bandage if it is not to keep on 

 geodesic lines. It is as a simple, necessary result of geodesic 

 principles that we see those " figures-of -eight " produced, to which, 

 in the case for instance of the heart-muscles, Pettigrew and other 

 anatomists have ascribed pecuhar importance. In the case of 

 both heart and stomach we must look upon these organs as de- 

 veloped from a simple cyhndrical tube, after the fashion of the 

 glass-blower, as is further discussed on p. 1049 of this book, the 

 modification of the simple cyhnder consisting of various degrees of 

 dilatation and of twisting. In the primitive undistorted cyhnder, 

 as in an artery or in the intestine, the muscles run in simple geodesic 

 fines, and constitute the circular and longitudinal coats which form 

 (or are said to form) the normal musculature of all tubular organs, 

 or the cylindrical body of a worm. However, we can often recog- 

 nise, in a small artery for instance, that the so-called circular fibres 

 tend to take a shghtly obhque or spiral course; and that the 

 so-called annular muscle-fibres are really spirals is an old statement 

 which may very hkely be true*. If we consider each muscular 

 fibre as an elastic strand embedded in the elastic membrane which 

 constitutes the wall of the organ, it is evident that, whatever be 

 the distortion suffered by the entire organ, the individual fibre will 

 follow its own course, which will still, in a sense, be geodesic. 

 But if the distortion be considerable, as for instance if the tube 



* See A Discourse concerning the Spiral, instead of the supposed Annular, 

 structure of the Fibres of the Intestins; discover'd and shewn by the Learn'd 

 and Inquisitive Dr. William Cole to the Royal Society, Phil. Trans, xi, pp. 603-609, 

 1676. Cf. Eben J. Carey, Studies on the. . .small intestine, Anat. Record, xxi, pp. 

 189-215, 1921 ; F. T. Lewis, The spiral trend of intestinal muscle fibres. Science, LV, 

 June 30, 1922. 



