STRUCTURE OP THE HUMAN BODY. . 45 



the wrist and ankle, have the bony matter extended over a 

 considerable space, in order in the most era^fijfcbfenner to 

 combine the properties of lightness and strength. The 

 whole assemblage constitutes an apparatus which is capable 

 of executing all the various movements that are necessary for 

 the purposes of life, with a degree of precision and velocity 

 that is truly wonderful. 



16. {The bones are covered with a fibrous sheathing of 

 dense membrane, called periosteum, which seems to nourish 

 the bone, for where it is abraded the bone perishes^ fit con- 

 tains an abundance of blood-vessels which run from it into 

 the bone ; besides these, a large blood-vessel enters the shafts 

 of the long bones near the centre, and branches out in each 

 direction, while numerous others enter at their extremities^ 

 These blood-vessels, though generally too minute to convey 

 the red particles of the blood, yet they readily transmit the 

 colouring matter of madder. Numerous experiments have 

 proved that when animals are supplied with food mixed with 

 that substance, in a few days |he bones are coloured red, or 

 of a pinkish colourjland on the discontinuance of it, in a 

 short time their natural colour is restored, showing the 

 rapidity with which deposition and absorption are carried 

 on in the healthy state. This is shown in cases of fracture, 

 where the broken ends of a bone become speedily united. I 

 have lately had a case of fractured thigh bone in a child, 

 where it became united with considerable firmness in one 

 week. 



17. stfarroiv is a species of fat deposited in the central 

 canals of the cylindrical bones, and in the lattice work of 

 the spongy bones!/ t is contained in the cells of a delicate 

 membranous web) and ;has been supposed by some to serve 

 as a reservoir of nourishment, and by others, to keep the 

 bones from becoming dry and brittle^ ^t is found in greater 

 quantity in thef adult and aged than in the youn^; in the 

 latter, indeed, its place is occupied by a gelatinous fluid. 



18. Chemical examination shows that{ bone is composed 



