KEMAKKS ON BONE-DEVELOPMENT. 361 



noted. Boussingault determined from his experiments that the 

 skeleton of a pig increases daily during the first eight months after 

 birth, about 2.9 drachms in weight (average) ; amounting to a for- 

 mation of about 1.55 drachm daily of osteine, and 1.35 drachm of 

 earthy matter, including .6 drachm of phosphoric acid. Subse- 

 quently to the eleventh month, the daily increase in weight averages 

 but 1.5 drachm daily ; there being only about .65 drachm of earthy 

 matter, including .35 drachm of phosphoric acid. 



2. Much discussion has arisen on the question whether bone is 

 always developed from cartilage those who maintain the affirma- 

 tive asserting that the blastema in which the periosteal layers of 

 the primary bones, and the whole of the secondary bones are deve- 

 loped, is also cartilage, but in its rudimentary stage of development. 

 It has already been seen that the cartilage-cells cannot at first be 

 distinguished from the primordial cells of other tissues. So far as 

 this fact is considered, therefore, it is as valid a proof of the assump- 

 tion that the blastema is a rudimentary collagenous, as that it is a 

 rudimentary cartilaginous tissue. The fact, however, that the iuter- 

 sutural substance contains no chondrine and never becomes cartilage, 

 though remaining till late in life, and finally ossifies, especially in- 

 ternally, without going through that change; it being, on the other 

 hand, white-fibrous tissue (the sutural ligament, p. 347) militates 

 against the idea that the secondary bones are developed from carti- 

 lage. Moreover, Kolliker appears to be correct in the assertion 

 that the periosteal layers of the primary bones are developed in 

 precisely the same manner. We, therefore, believe with him 

 against Meyer and many other histologists that while the cancel- 

 lated substance of the primary bones is developed in cartilage, the 

 secondary bones, as well as the periosteal layers of the primary, are 

 developed in a matrix homologous with white fibrous tissue. 



Indeed, if we trace the development of the skeleton through the 

 animal series, we find, 1, that in all vertebrated animals those parts 

 of it requiring some degree of firmness during the early periods of 

 development, consist of cartilage; while the rest is developed from 

 a softer substance. The cartilaginous portion will constitute more 

 or less of the whole future skeleton, according to the habits, &c., of 

 the animal ; e. g. the cranium of the pig is more exclusively carti- 

 laginous than the human cranium. 2. In some of the lowest ver- 

 tebrata (cartilaginous fishes), the skeleton remains in the cartilagin- 

 ous state through life. 3. In all the land vertebrata, however, a 



