348 Mr. H. G. Secloy on a Theory 



come larger still. la this class, as in the subclass Saurornia, 

 founded on the Pterodactyles, the process goes on till even the 

 marrow disappears in the bones most used in motion, and their 

 wonderfully thin walls become filled with hot air from tlie 

 lungs. 



Now it becomes necessary to consider in what manner pres- 

 sure from muscles and other internal forces can act on the bones 

 so as to produce growth ; and here I would draw the illustration 

 from pathology. Inflammation, in effect, is pressure; and 

 whenever inflammation extends to the periosteum, that struc- 

 ture is excited to a morbid rapidity of action, and the bone 

 immediately beneath is thickened : hyperostosis is defined to be 

 a thickening and condensation of the shaft from inflammation. 

 Nor is the pathology of the heart and the lung less suggestive 

 where it shows, as is well known, that muscle may be inflamed, 

 indurated, and changed into cartilage, which undergoes a partial 

 change into bone, though, from the nature of the case, the last 

 change can never advance very far, except in the lung, which 

 may be replaced by muscle and well-developed bones. 



Therefore, seeing that the eff^ect of motion is a succession of 

 falls, every one of which gives a powerful blow to the bones, and 

 that no muscle can be moved without both pulling and pressing 

 bones, we have an irritating cause, similar in kind though less 

 in degree to that which results in abnormal growth. And 

 accordingly it is found that the greater the activity (that is, the 

 nearer the approach to an inflammatory condition) the more 

 extensive will be the ossification. 



Thus in the wild animal, which uses its muscles more vigo- 

 rously than the tame animal, the ridges and processes for the 

 attachment of muscles are more developed. In the limbs a 

 trochanter appears as a separate ossification, where powei-ful 

 muscles are attached. The marsupial muscles, which are small 

 in man, become largely developed in the Didelphia, and create 

 the marsupial bones. 



Now it remains to show that the intensity of growth depends 

 on the amount of the pressure and tension in the direction of 

 the increase. Dr. Humphrey tells us that bones are densest in 

 those parts which are subject to the greatest mechanical stress, 

 and hardest in those persons who are strongest and most active. 

 Here the intensity of ossification clearly depends on the pres- 

 sure. And, again, ic is observed that bones are most curved in 

 those persons whose muscular strength is greatest — that is to 

 say, where the pressure resulting from muscular action is the 

 greatest; while weak persons, on the contrary, have compara- 

 tively straight bones. And thus it is seen that, even in the 

 individual, the form of the bone varies with the relative power 



