10 DK. BEALE, ON THE TISSUES. 



culatiou of tluids holding the calcareous matter in solution is 

 maintained^ and thus the extreme regularity with which the 

 growth of the tissue occurs is ensured. 



For some time after the first deposition of the calcareous 

 matter in the formed material, very thin fragments of the 

 bone torn away exhibit the appearance of fibres (a fact pointed 

 out many years ago by Dr. Sharpey), in the substance of 

 which globules have been deposited, but slowly the calcareous 

 matter becomes more homogeneous, in consequence, probably, 

 of changes occurring in its substance, and its more perfect 

 incorporation with the organic matrix, and ultimately the 

 hard mass appears even in texture, uniformly transparent, 

 and penetrated everywhere by minute tubes. 



It seems to Dr. Beale that these tubes are the altered 

 spaces which are left between the calcareous globules origi- 

 nally deposited. They were at first triangular in outline, but 

 gradually they have become altered by the filling up of the 

 angles, until at last they become pores, the section of which 

 is nearly circular. From appearances the lecturer has seen in 

 some preparations of the bones of the frog^s skull (frontal, 

 parietal), he feels sure that in this case the bone results from 

 changes in the original cartilage ; the nucleus of the cartilage 

 cell remaining as the nucleus in the lacuna. The calcareous 

 matter deposited in the matrix around a cartilage cell under- 

 goes changes, probably sloAvly becomes incorporated with the 

 organic matter, and gradually ceases to exhibit the appearance 

 of being composed of separate masses, and becomes more 

 homogeneous. The spaces become canaliculi, and the mass 

 at last assumes the structure of perfect bone. 



For some time separate calcareous particles are seen within 

 the outline of the lacuna, which gradually diminishes in size 

 as calcareous matter is deposited in the matrix from without 

 inwards. This point was represented in a drawing which 

 showed about one-third of the inner part of a recently-formed 

 lacuna of the frog, magnified 1700 diameters. A part of the 

 nucleus is seen in the lower part of the drawing. 



In the development of the long bones of mammalia, on the 

 other hand, it is equally certain that the spongy, imperfectly 

 formed bone at first developed is gradually removed, and gives 

 place to new bony tissue of a more perfect structure not 

 formed from cartilage, while, as is well known, there are 

 examples of the formation of bone without the existence of 

 cartilage at any period, in the case of certain bones of the 

 cranium. 



Kolliker considers that the capsule of the cartilage cell and 

 the matrix become impregnated with calcareous matter, while 



