4 THE SKELETON 



totrethor by a delicate reticulum of connective tissue; the space containing' the 

 marrow is the medullary cavity. The expanded ends of the bone contain a network 

 of eancellous tissue, the spaces being filled with red marrou: This cancellous tissue 

 differs from that of the f(etal bone in that it is arranged in a definite manner accord- 

 ing to the direction of pressure and the tension exerted Ity muscles. Pressure 

 lines are Avcll shown in the vcrtebne. In a vertical section through the centiuiu i)t' 



Fk;. J. — a Yekteukal Cextklm ix sectiox to show the Pressukk Ccrves. 



a vertebra the fibres of the cancellous tissue are seen to be arranged vertically and 

 horizontally ; the vertical fibres are curved with their concavities directed tOAvards 

 the centre of the bone. The horizontal fibres are slightly curved parallel with the 

 upper and lower surfaces, with their convexities towards the centre of the bone. 

 They are not so defined as the vertical set. ( Wagstaffe. ) 



The arrangement of the cancelli in individual l)ones is a consequence of the 



Fig. 3. — A Diagram nt show the 

 Pressire and Texsiox Curves of 

 the Femur. (After Wagstaffe.) 



Fig. 4. — A Diagram showing Pres- 

 sure axi) Texsiox Curves in 

 the Head of the Humerus. (After 

 Wagstaffe. ) 



mechanical conditions to which the hone is subject. This is well illustrated in the 

 femur. In the u])per end of this bone, the cancellous tissue is arranged in 

 divergent curves. One set springs from the inner wall and spreads into the greater 

 trochanter; a second series of curves crosses this and forms a set of Gothic arclu's, 

 and is continued into the neck and head; a third set springs from the lower thick 

 wall of the neck and s]»reads into the up))er part of the head, and ends perpen- 

 dicularly in the articular surface mainly along the lines of greatest pressure. A 



