Preliminary 



which their blood supply reaches them ; thus, whereas the stripping of the shaft of a 

 long bone will result in necrosis of the exposed osseous tissue, the bones of the cranial 

 vault may be laid quite bare without such result, because their blcod supply is almost 

 wholly derived from the meningeal vessels on their deep surface. 



Before the student starts on the study of the details of the skeleton he should 

 have some knowledge of the factors that are responsible, in each individual bone, for 

 the appearance it presents in the adult state. The following considerations ought 

 therefore to be understood, for on the comprehension and appreciation of their bearing 

 on any particular bone will depend the student's ultimate grasp of the bone and its 

 possible modifications : he must, moreover, bear in mind that a knowledge of bones 

 and muscles and intermuscular planes is essential to a proper understanding of the 

 anatomy of the body, that the planes of muscles cannot be properly grasped without 

 study of the skeleton, that the bones are only incompletely studied without the 

 muscles and soft parts in relation with them and attached to them, and that many of 

 the smaller details of the structure of the body that puzzle the student can be solved 

 at once by an intelligent appeal to the skeleton. The principal factors responsible 

 for the appearance of the adult bones are most easily illustrated in the long bones of 

 the limbs ; but the student must 



remember that they are also opera- A - R4 



tive in the other bones, and as his 

 studies proceed he should endeavour 

 to see how they have come into 

 action in these other instances. 



i. The shape and moulding of 

 the surfaces of a bone depend on 

 two main factors (a) its primary 

 " build " for performing certain 

 functions and to resist certain 

 strains, and (b) secondary mould- 

 ing resulting from the arrange- 

 ment and " pressure " of the sur- 

 rounding structures. Thus in the fibula there is a strong bar of bone running 

 throughout its length that is of a primary nature and remains in itself unaltered by the 

 various structures attached to it, but it is covered in and partly hidden by secondary 

 surfaces moulded over it and shaped by the covering muscles, and it can only be 

 recognised here and there through some of these surfaces, making a convexity where 

 there would otherwise be flatness or a concavity : again, in the lower jaw, we have 

 the angled shape as a necessity of function, to bring the teeth into opposition, and 

 combined with this as other primary constructions there are (see Fig, 210) the thick 

 splenial portion to support the down- push of the alveolar part that carries the teeth, 

 and the existence of a thick bar to counteract the tendency of the angle to open out ; 

 while on these and not affecting them we find the secondary moulding shown, for 

 example, in the presence of glandular fossae and a coronoid process. Or in the scapula 

 a thick bar (see p. 70) extends from the lower angle to the glenoid process, and its 

 relation to the axillary border varies individually in detail, because the border is a 

 secondary one which varies with the development of the Subscapularis that makes it, 

 whereas the bony bar is quite unaffected by the muscles that lie over it. Considerations 

 such as these will enable the student who endeavours to understand their bearing to 

 comprehend the meaning of the existence and appearance of the various surfaces 

 seen on a bone, to appreciate the way the bone lies in relation to surrounding 



FIG. 4. Schematic sections through the fibula at various 

 levels from above down, to show how the primary 

 cylindrical bar of the bone is overlaid and hidden 

 by the mouldings due to the muscles applied to it. 

 The dotted line covers the Peronei r A.P.S. ia the 

 anterior peroneal septum, int. the interosseous mem- 

 brane, and T.P.A. is the aponeurosis covering Tibialis 

 posticus. 



