16 OSTEOLOGY. 



ary Haversian canal, no trace being left of the nucleus of the 

 original cartilage corpuscle ; but there are numerous very minute 

 reddish' gi^anules, which almost fill the cavity, and are concerned 

 in the form^-tion of blood-vessels, which now begin to appear. 

 The oSsific . parietes of the cartilage cells lining the tube, at first 

 thin, enlarge and thicken by successive layers of dense osseous 

 matter, and thus produce the concentric lamellae, the lamella last 

 formed pushing out the older one, until what was the lining of 

 the tube becomes the external lamella of an Haversian system, 

 while the ossific matter which was deposited in the column of 

 intercellular material, becomes the connecting lamellae between 

 the Haversian cylinders. 



In long bones this ossific process commences in the centre of 



Fia. 5. 



Section of ossifying cartilage magnified. On the left the ceils are 

 becoming arranged in rows ; while to the rights between the rows, the 

 earthy material is being deposited. 



the shaft, gradually spreading to the extremities, in which there 

 are separate points of ossification ; there are generally three such 

 points, one for the shaft, and one for euch extremity, the develop- 

 ing shaft being called the diaphysis, the extremities the epiphyses. 

 When any process is supera'dded, as the trochanter of the femur, 

 \ which possesses a distinct point of ossification, it may be termed 

 \&IL apophysis. As ossification commences in the shaft, there are 

 ibr some time after birth, intervening portions of unossified 

 ■ cartilage, marked by a deep ring in the dried long bones of 

 young animals ; they disappear at variable periods, the portions 

 of bone hitherto imperfectly united becoming consolidated into 

 one firm mass. The bone increases in length by growth of the 

 unossified ring, uniting the shaft and epiphysis, until the ring fills 

 up, when growth is completed. Should an epiphysis unite with 

 the diaphysis prematurely, by acceleration of the process of ossifi- 

 cation through disease, growth being thus arrested, the bone will be 

 shorter than its fellow. The shaft of a long bone increases in 



