276 Mr. H. G. Seeley on the Origin 



sternal ends of the clavicles ; but they are not there in child- 

 hood while growth is going on in a normal way, but are only 

 developed when the chest is undergoing its greatest lateral 

 expansion, in the years from 17 to 20, when they become 

 anchylosed to the shaft of the bone. And in many heavy- 

 bodied active animals, like the buffalo, rhinoceros, &c., the rib 

 terminates at its head in an epiphysis, which articulates with 

 another epiphysis on the neural arch ; while in light-bodied 

 animals no such epiphyses are met with. And wherever epi- 

 physes are found, whether as terminal of bones or as places 

 for the attachment of powerful muscles, it is only where pres- 

 sure and tension are manifested under conditions of great 

 activity of the part. This new bony growth takes place to- 

 wards the articular termination of the cartilage, where the 

 subinflammatory condition is induced by local activity — and 

 so, while giving a means for the articular ends of bones to 

 become better adapted to each other, protects the epij^hysial 

 cartilage and furnishes it with an additional surface on which 

 bony growth may take place. From which considerations it 

 would appear that one ossification may develope another upon 

 itself whenever the forces manifested at its ends (or elsewhere) 

 are more than sufficient to continue simple growth by increase 

 on the normal surface. Small ossifications are often met with 

 about the joints in many parts of the body, which have origi- 

 nated in this way. The fact of epiphyses being only charac- 

 teristic of certain species of animals in each class shows us 

 that they have no necessary connexion with the animal grade 

 of organization ; the fact of their appearing under conditions 

 of unusual activity shows that their origin is the same as that 

 of all other bones, but that they are of subordinate importance 

 in the skeleton, since they become united to the normal ske- 

 letal elements, and do not necessarily modify the form of their 

 terminal ends. 



I now notice the general morphology of bones and its rela- 

 tion to mechanical causation. 



Mr. Charles Darwin finds that the domestic races of pigeons, 

 fowls, and ducks, which fly little, have the chief bones to which 

 are attached the muscles which are exercised in that function 

 smaller and lighter than in the parent races. Similarly it is 

 observed that, in the improved races of pigs, shortened legs 

 and snout, and altered form of the occipital condyle, may be 

 attributed to the parts not having been fully exercised ; for 

 the highly cultivated races do not travel in search of food 

 nor root up the ground with their ringed muzzles. Also 

 domestic rabbits have the body and whole skeleton larger 

 and heavier than the wild animal, and the leg-bones are 



