GROWTH OF BONES. 71 



In some of the flat bones, as the sternum and the sacrum, 

 there are, first of all, a great many distinct points of ossification, 

 which quickly unite into a smaller number ; they then remain 

 stationary for a number of years, but finally all unite into but 

 one piece. 



The ossification of the thick bones begins by one or more 

 points, according to the simplicity or complexity of their figures. 

 The bones of the tarsus and of the carpus, have each but one 

 point, while those of the spine have several. The two former, 

 as stated, are almost entirely cartilaginous at birth. The re- 

 maining phenomena of ossification in these several bones are the 

 same as has been mentioned. 



SECT. II. ON THE MANNER IN WHICH BONES GROW. 



After the cartilaginous condition of the bones has been sup- 

 plied by the complete deposite of osseous matter, and they are 

 finished, with the exception of the epiphyses being fused into the 

 respective bodies, the bones still continue to grow till the indi- 

 vidual has reached a full stature. This is effected by the succes- 

 sive addition of new matter to the old. The long bones lengthen 

 at their extremities; this is proved by the following experiment 

 of Mr. John Hunter.* Having exposed the tibia of a pig, he 

 bored a hole into each extremity of the diaphysis, and inserted 

 a shot; the distance between the two shots was then accurately 

 taken. Some months afterwards, when the animal had increased 

 considerably in size, the same bone was examined, and the shots 

 were found precisely at their original distance from each other, 

 but the extremities of the bone had extended themselves much 

 beyond their first distance from the shots. The flat bones in- 

 crease in breadth by a deposite at their margins, a circumstance 

 which has been known a long time, but it required the ingenui- 

 ty of Mr. Hunter to prove conclusively that the long bones in- 

 crease in length by a similar process, and not by interstitial de- 

 posite, as Duhamel thought. This observation explains most 

 satisfactorily the use of the cartilage between the diaphysis and 

 the epiphysis in all bones ; that it is merely interposed for the 



* Transactions of a Society for Improvement, vol. ii. London, 1800. Experi- 

 ments and Observations on the Growth of Bones. 



