S20 On the f7>e of the Sutures 



bones merely" by periosteum, at that part 

 osseous materials are added to increase theii: 

 length or extend their superficies. This we 

 shall find takes place, whether the junction be 

 effected by comparatively smooth surfaces, as 

 between the body of a bone and its epiphysis; 

 or between the bones of the skull by jagged 

 sutures. Hence' it. appears that the bones 

 of the body generally are increased in 

 length or extent, not by a uniform exten- 

 sion of the whole substance, but by an ad- 

 dition of bony matter in some particular 

 part. 



Thus the body of a cylindrical bone is 

 lengthened by addition to each end. This 

 we might conclude would be the case from 

 considering the part, in which its ossification 

 commences: as this commences in a middle 

 point and proceeds to each extremity, it is 

 uatural to suppose that its growth still goes on 

 in the same direction, or continues at the ex- 

 tremities. That this is the case we know, not 

 by reasoning alone, but by a direct experimeat. 

 Mr. Hunter sunk two small pieces of lead in 

 the middle of the tibia, or shin bone of a pig, 

 amid measured accurately the distance between 

 them : on examining the animal some time 

 afterwards, it appeared, that though the bone 

 had increased considerably in length, tlie 



