205 



In the circumferential lamince are frequently found elongated tubes 

 which the authors regard as modifications of lacunae ; they run ob- 

 liquely across the laminae, generally in bundles. They frequently 

 form communications with the canaliculi. In transverse section 

 they are seen to have proper walls. 



4. Haversian systems. — The authors have here pointed out that the 

 anastomosis of the canaliculi of adjoining systems is rare in newly- 

 developed systems, but is very common in those of greater age. It 

 has been seen too that it not unfrequently happens that a series of 

 Haversian systems is contained within a common series of surround- 

 ing laminae. Sometimes the Haversian systems are rendered quite 

 solid by the narrowing of the Haversian canal and ultimate develop- 

 ment of a mere lacuna in the centre of the system. The more re- 

 cently developed Haversian systems which occupy Haversian spaces 

 are seen to be darker in colour than the older ones, from the greater 

 abundance of canaliculi, and the more general granularity of the 

 tissue. 



5. Ossified articular cartilage. — This structure the authors have 

 found in all the joints which they have examined, in the lower jaw, 

 amongst others, where Kolliker failed to detect it. Towards the 

 bone the tissue becomes in general granular and of a brownish colour, 

 and usually there is a distinct lii^ of demarcation between the bone 

 and the ossified cartilage ; but sometimes they graduate insensibly 

 the one into the other. 



Towards the articular surface the margin is even and regular ; but 

 towards the bone it is deeply indented, from the bone advancing into 

 it by rounded projections. Hence the articular cartilage varies in 

 thickness. The authors believe that this, so far from being an indi- 

 cation of imperfect development, is in reality an evidence of design, 

 and intended to give an uniform and unyielding surface for the car- 

 t^ilage to rest upon. 



6. Ossified cells. — In the bones of aged people it is frequently ob- 

 serv-ed that they become light and spongy, and after maceration con- 

 tain a white powder in the cancellated structure. This powder the 

 authors have found to be composed mainly of ossified nucleated 

 cells, either detached or held together in masses. They are spherical, 

 and contain a dark granular nucleus, which is surrounded by a thick 

 transparent wall. 



If portions of the cancelli be taken, they will be found to have simi- 

 lar cells adherent to their surfaces, or to those of the Haversian 

 canals, with here and there canaliculi of adjoining lacunse shooting 

 into them, while the nuclei have themselves assumed the form of 

 lacunae. Similar cells maybe found imbedded in parts of most sec- 

 tions of bone. In order to see this condition clearly, it is desirable 

 that the sections and the loose cells should be mounted in Canada 

 balsam. 



7. Bone tissue. — The views generally entertained with regard to the 

 ultimate structure of bone tissue are, the older one, that it consists 

 of an aggregation of granules in a transparent matrix ; and that 



