FORMATION OF BONE. 201 



ments and observations, for I really feel more interest in 

 this account of the bones than I had anticipated. 



Dr. B. Attend then, with all patience, to a few re- 

 marks on the formation, nutrition, and restoration of 

 bone. We may examine an animal in the first periods of 

 existence the chick in the egg, for instance and ob- 

 serve the general shape of the body and the rudiments of 

 limbs, but find no traces whatever of bone. In their 

 place, we observe a soft, semi-fluid substance contained 

 within a delicate membrane. This, after a time, as- 

 sumes the consistency of cartilage, transparent, and col- 

 ourless, but possessing the form of the future bone. Next, 

 the vessels which before carried only white fluids, en- 

 large and give admittance to the red particles, and the 

 first mark of ossification may be considered this appear- 

 ance of a little artery, filled with red blood, pursuing its 

 way into the substance of the cartilage. Other arteries 

 appear in it from different directions, overtake the first, 

 and finally form a net-work of minute vessels. Here 

 bony matter is deposited from the mouths of these ves- 

 sels, and at length we have a little centre or nucleus of 

 ossification, spreading in the form of fine rays, in all di- 

 rections. In this manner, arteries appear in other parts 

 of the cartilage, and form centres of ossification, which 

 spread and meet each other, and thus the whole bone is 

 completed. In the long boues, there aie several cen- 

 tres of ossification ; the body and each extremity re- 

 ceive a set of vessels which enter it by a common trunk; 

 and these parts are each perfectly formed before they 

 are united together indeed, in some of the bones, they 

 remain several years after birth, before they are united 

 by any thing more than cartilage. 



Such is the way in which bones are always formed ; 

 the plan is first laid in cartilage an isolated mass, with- 

 out holes or cavities and is afterwards moulded into its 

 proper forms, during the process of ossification. The 

 cartilage, you see, is not hardened, nor converted in any 

 way into bone, as the older physiologists believed, for 



