THE CONNECTIVE SUBSTANCE GKOUP. 99 



At first the bone is spongy, but later absorption takes place 

 osteoporosis. Around some of the marrow- tubes concentric 

 lamellae are formed, and in this way a Haversian system de- 

 velops. The unabsorbed portions of the trabeculae are thought 

 to constitute the lamellae known as the intermediary. Com- 

 pact tissue is thus formed from spongy. This theory, which 

 has been placed in its present acceptable light by Klein, is very 

 simple and appears to accord with observation, and explains 

 all the phenomena. Yet those' who have believed in the direct 

 transmutation of cartilage into bone are still in the field. 

 Kolliker maintains that both views are correct. 



According to this last named author the differences between primary or 

 primordial and the tegumentary or secondary bones are, from a morphological 

 point of view, sharp and complete. The former are ossifications of the carti- 

 laginous skeleton. 



The tegumentary are never cartilaginous at first ; the primordial bones, on 

 the other hand are, without exception, formed from cartilage. The method and 

 manner in which bony tissue is formed is the same in both bones. The pri- 

 mordial skeleton in the lower vertebrates ossifies only in part from the peri- 

 chondrium, in part perichondrally, and, in part, endochondrally. 



According to Kassowitz, in the tuberosities and spines of the bones the 

 periosteal processes of the periosteum, which develop the bone, are primarily 

 cartilaginous, the fibrillated tissue being converted into hyaline cartilage, 

 which is at first calcified and then undergoes direct conversion into bone. 



According to the experiments of Strawinsky a transplanted periosteum will 

 develop either bone or cartilage, when the conditions are favorable. The con- 

 ditions of nutrition determine which it shall be. When the supply is best, 

 cartilage is formed ; when poorest, bone. 



The earliest evidences of ossification were seen by this observer between 

 the fourth and fifth days. The formation of vessels preceded that of bone. 

 Absorption commenced between the second week and the second month. The 

 new formation of periosteum is partly derived from the border of the wound 

 and partly from the Haversian canals, which contain a small amount of connec- 

 tive tissue. 



Development of bone and absorption. It has been seen 

 that these two processes go on hand in hand. As soon as the 

 periosteum has commenced to deposit new layers of bone on 

 the surface of the primary spongy bone, absorption takes place 

 along the marrow canal. First of all, as we have already said, 

 the innermost of the concentric lamellae yield. In this way 

 the Haversian canals are widened and become Haversian spaces, 

 as they were at first ; then the interstitial lamellae, and finally 



