72 SKELETON. 



purpose of offering the least possible resistance to the new os- 

 seous fibres, which grow from the epiphyses and from the dia- 

 physes: and that it is kept for this end, without any material 

 change in thickness, from the fourth or fifth year to the six- 

 teenth or eighteenth, when it disappears, because there is no 

 longer any use for it, in consequence of the bones having at- 

 tained their full length. 



The epiphyses are then manifestly intended to favour the 

 elongation of the bodies and the development of the extremities 

 of the long bones, to suit the same purposes in some of the flat 

 bones, as those of the pelvis, and to permit the general deve- 

 lopement of the bodies of the vertebras. The ossification of the 

 epiphyses commences in some bones about fifteen days before 

 birth, as in the inferior extremity of the thigh bone, and in 

 others, as those of the ossa innominata, not till the fifteenth 

 year or thereabouts. Many of the processes from the bones, 

 are also epiphyses, as the trochanters of the os femoris, the 

 tuber of the ischium, the acromion scapulae, the seven processes 

 of a vertebra, and so on, and are developed in the same way. 

 The time at which they all are thoroughly fused into the bones 

 to which they belong, extends from the fifteenth to the twenty- 

 fifth year; depending upon the individual bone, and upon vari- 

 eties of constitution in different persons : though this process 

 may be considered as completed, generally, in the female at 

 the age of eighteen, and in the male at twenty-one. 



The increase in thickness of every bone depends upon a 

 continued secretion from the internal surface of the periosteum, 

 at first soft and mucous, then osseous : when this secretion is 

 arrested, the bones cease to grow in thickness, which com- 

 monly occurs some time after they have attained their full 

 length. The changes which subsequently take place in them 

 are those of interstitial deposite and absorption : the former is 

 well exemplified in inflammation of the bones, and in spina 

 ventosa ; the latter in the diminution of the bones in extreme 

 old age, and in the loss of the alveolar processes. 



There is no period of life in which this interstitial absorption 

 and deposite is not continually occurring, but it is much more 

 rapid in young and growing animals than in the adult and old. 

 The experiments of Mr. Hunter and of Duhamel, show, that 

 when a growing animal is fed upon madder, (rubia tinctorum,) 



