280 BONE OR OSSEOUS TISSUE. 



epiphyses thus formed are separated, as long as growth continues, from the shaft or 

 diaphysis by an intervening portion of cartilage, which is at last ossified, and the 

 bone is then consolidated. 



A remarkable exception to the ordinary mode of ossification of the cartilage-bones 

 occurs in the terminal phalanges of the digits. In these the calcification of the 

 cartilage begins at the distal extremity or tip, and the sub-periosteal deposit appears 

 simultaneously at the same point, and forms a cap-like expansion over the end of the 

 phalanx. The irruption of the osteoblastic tissue also first occurs at this place. The 

 expanded portion of the phalanx which bears the nail is formed independently of 

 cartilage (Dixey). 



Growth and absorption of bone. The time of final junction of the 

 epiphyses is different in different bones ; in many it does not arrive until the body 

 has reached its full stature. Meanwhile, as above described, the bone increases in 

 length by the ossification continuing to extend into the intervening cartilage, which 

 goes on growing at the same time ; and it appears that in the part of the shaft 

 already ossified little or no elongation takes place by interstitial growth. 1 This is 

 shown by an experiment first made by Hales and afterwards by Duhamel and by 

 John Hunter, in which, two or more holes being bored in the growing bone of a 

 young animal at a certain measured distance from each other, they are found after 

 a time not to be farther asunder, although the bone has in the meanwhile consider- 

 ably increased in length. On the other hand, if one hole be bored in the epiphysis 

 and another in the shaft, they become distinctly removed from one another with the 

 growth of the bone. Moreover, it is well known that if the intervening cartilage in 

 growing bone be injured by disease or removed by the knife, the growth of the bone 

 in length permanently ceases. 



Both Hales and Duhamel in experimenting on the growing tibia of a chicken, 

 observed that the elongation was much greater at the upper end. Humphry has 

 shown that in the arm-bones the elongation is greater at the end furthest from the 

 elbow joint, and in the leg-bones at the end which is next the knee joint. 



In the human subject between the first and the fourth or fifth years, the long 

 bones grow chiefly in length, scarcely at all in thickness. 



The shaft of a long bone increases in circumference by deposition of new bone 

 on its external surface, while at the same time its medullary canal is enlarged by 

 absorption from within. This can be determined by two methods of experimenting. 

 Thus, in the first place, a ring of silver or platinum put round the wing-bone of a 

 growing pigeon, becomes covered with new bone from without, and the original bone 

 included within it gets thinner, or, according to Duhamel, who first made the experi- 

 ment, is entirely removed, so that the ring comes to lie within the enlarged medul- 

 lary canal. Secondly, madder given to an animal along with its food tinges those 

 parts in which deposition of new bone is taking place. The earth of bone appears 

 to act as a sort of mordant, uniting with and fixing the colouring matter ; and, as 

 in this way the new osseous growth can be readily distinguished from the old, advan- 

 tage was taken of the fact by Duhamel, and afterwards by Hunter, in their inquiries 

 as to the manner in which bones increase in size. By their experiments it was shown 

 that when madder is given to a young pig for some weeks, the external part of its 

 bones is deeply reddened, proving that the new osseous matter is laid on at the 

 surface of that previously formed. Again, it was found that, when the madder was 

 discontinued for some time before the animal was killed, an exterior white stratum 

 (the last formed) appeared above the red one, whilst the internal white part, which 

 was situated within the red, and had been formed before any madder was given, had 



1 The occurrence of a certain amount of interstitial expansion is strenuously upheld by J. Wolff (see 

 Bibliography). 



