X] ON GEODETICS 491 



is evident that, whatever be the distortion suffered by the entire 

 organ, the individual fibre will follow the same course, which wil) 

 still, in a sense, be a geodetic. But if the distortion be consider- 

 able, as for instance if the tube become bent upon itself, or if at 

 some point its walls bulge outwards in a diverticulum or pouch, 

 it is obvious that the old system of geodetics will only mark the 

 shortest distance between two points more or less approximate to 

 one another, and that new systems of geodetics will tend to 

 appear, pecuhar to the new surface, and linking up points more 

 remote from one another. This is evidently the case in the 

 human stomach. We still have the systems, or their unobliterated 

 remains, of circular and longitudinal muscles; but we also see 

 two new systems of fibres, both obviously geodetic (or rather, 

 when we look more closely, both parts of one and the same 

 geodetic system), in the form of annuli encircling the pouch or 

 diverticulum at the cardiac end of the stomach, and of oblique 

 fibres taking a spiral course from the neighbourhood of the 

 oesophagus over the sides of the organ. 



In the heart we have a similar, but more complicated 

 phenomenon. Its musculature consists, in great part, of the 

 original simple system of circular and longitudinal muscles 

 which enveloped the original arterial tubes, which tubes, after 

 a process of local thickening, expansion, and especially twisting, 

 came together to constitute the composite, or double, mammalian 

 heart; and these systems of muscular fibres, geodetic to begin 

 with, remain geodetic (in the sense in which we are using the 

 word) after all the twisting to which the primitive cylindrical tube 

 or tubes have been subjected. That is to say, these fibres still 

 run their shortest possible course, from start to finish, over the 

 complicated curved surface of the organ; and it is only because 

 they do so that their contraction, or longitudinal shortening, is 

 able to produce its direct effect, as Borelli well understood, in 

 the contraction or systole of the heart*. , 



* The spiral fibres, or a large portion of them, constitute what Searle called 

 "the rope of the heart" (Todd's Cyclopaedia, n, p. 621, 1836). The "twisted 

 sinews of the heart " were known to early anatomists, and have been frequently 

 and elaborately studied : for instance, by Gerdy (Bull. Fac. Med. Paris, 1820, 



