334 



THE ANIMALS AND MAN 



Tmj 



the periosteum, which is bone- 

 forming material. Surfaces 

 for articulation with other 

 bones are smooth and covered 

 with cartilage (Cpl,Tr and Cp) . 



A bone, sawed through the 

 middle, as shown in fig. 170, 

 exposes a dense layer of hard 

 bone (b) enclosing, at the 

 ends, a spongy mass of bone 

 tissue (c), the spaces of which 

 are filled with red marrow. 

 Here red blood corpuscles are 

 formed. The shaft encloses 

 a space filled with yellow 

 marrow (a). This is rich in 

 fat and gelatin. This struc- 

 ture secures the maximum 

 of strength for a given amount 

 of bone material. In the ribs, 

 or other flat bones, the entire 

 outer wall is dense and hard, 

 while the entire central part 

 is made up of a spongy mass 

 of bone filled with red marrow. 



Chemical composition of 

 bone. — Bone is formed from 

 materials taken into the body 

 with the food, chiefly lime, 

 salts (mineral matter) and 



Fig. 169. Right humerus seen from 

 in front. Cp, rounded surface of 

 upper extremity; Tr, Cpl, round- 

 ed surfaces of lower extremity. 



Tmj, Tm, El, Em, prominences for attachment of muscles; Aa (x— z) 



central shaft. (After Martin.) 



