XVI] THE STRUCTURE OF BONE 675 



bridge, for instance, a great part of the fabric is subject to tensile 

 strain only, and is built throughout of ropes or wires; but the 

 massive piers at either end of the bridge carry the weight of the 

 whole structure and of its load, and endure all the " compression- 

 strains" which are inherent in the system. Very much the 

 same is the case in that wonderful arrangement of struts and ties 

 which constitute, or complete, the skeleton of an animal. The 

 "skeleton," as we see it in a Museum, is a poor and even a mis- 

 leading picture of mechanical efficiency*. From the engineer's 

 point of view, it is a diagram showing all the compression -hues, 

 but by no means all of the tension-hnes of the construction; it 

 shews all the struts, but few of the ties, and perhaps we might 

 even say 7ione of the principal ones ; it falls all to pieces unless 

 we clamp it together, as best we can, in a more or less clumsy and 

 immobihsed way. But in hfe, that fabric of struts is surrounded 

 and interwoven with a compUcated system of ties : hgament and 

 membrane, muscle and tendon, run between bone and bone; 

 and the beauty and strength of the mechanical construction he 

 not in one part or in another, but in the complete fabric which 

 all the parts, soft and hard, rigid and flexible, tension-bearing 

 and pressure-bearing, make up together f. 



However much we may find a tendency, whether in nature or 

 art, to separate these two constituent factors of tension and 

 compression, we cannot do so completely; and accordingly the 

 engineer seeks for a material which shall, as nearly as possible, 

 offer equal resistance to both kinds of strain. In the following 

 table— 1 borrow it from Sir Donald MacAlister — we see approxi- 

 mately the relative breaking (or tearing) hmit and crushing Hmit 

 in a few substances. 



* In preparing or "macerating" a skeleton, tlie naturalist nowadays carries 

 on the process till nothing is left but the whitened bones. But the old anatomists, 

 whose object was not the study of "comparative" morphology but the wider 

 theme of comparative physiology, were wont to macerate by easy stages; and in 

 many of their most instructive preparations, the ligaments were intentionally left 

 in connection with the bones, and as part of the "skeleton." 



t In a few anatomical diagrams, for instance in some of the drawings in 

 Schmaltz's Atlas der Anatomie des Pferdes, we may see the system of "ties" 

 diagrammaticaUy inserted in the figure of the skeleton. Cf. Gregory, On the 

 principles of Quadrupedal Locomotion, Ann. N. Y. Acad, of Sciences, xxn, p. 289, 

 1912. 



43—2 



