204 



6. Ossified cells. 



7. Bone tissue. 



8. Development of bone in temporary cartilage. 



9. Growth of bone. 



1. Haversian and other canals of bone. — Besides the Haversian 

 canals, the authors have pointed out that there are found in bone 

 sections spaces of an entirel}^ different character, irregular in shape, 

 and with an irregular festooned margin. Their margins correspond 

 in outline with those of one or more Haversian systems, and precede 

 in many instances the formation of those systems. These spaces 

 produced by absorption are called by the authors Haversian spaces. 

 Unlike the Haversian canals which are surrounded by their own 

 laminae, these spaces are bounded by parts of several systems which 

 have been enci cached on by the process of absorption. 



In examining various sections, or different parts of the same 

 section, these spaces will be found in different states of partial or 

 entire occupation by Haversian systems. They are found in the 

 bone of subjects of all ages. The fact of removal of old tissue and 

 replacement by new, which has been hitherto only assumed, is thus 

 demonstrated. 



2. LamincB of hone. — Lamination is shown to be a constant character 

 of mammalian bone ; each lamina, when highly developed, is found 

 to consist of a dark granular, and of a transparent part. The ex- 

 ternal margin of the outermost lamina of each Haversian system is 

 irregularly indented and corresponds with the outline of a pre-exist- 

 ing Haversian space ; while its internal margin and all the succeed- 

 ing laminae are regular in outline. 



The laminae are found as a general rule to surround their canal, 

 which is usually placed in the centre of them. But sometimes the 

 canals are eccentric, in which case either the laminae on one side, 

 though still surrounding the canal, are broader, or there are more 

 developed on one side than on the other. The lamina next to the 

 perfected Haversian canal however is always complete, and is often 

 composed of a transparent structureless tissue, like that which encir- 

 cles the Haversian canals of the stag's antler at the time of shedding. 



The presence of interstitial laminae is readily accounted for ; they 

 are in fact the remains of pre-existing Haversian systems, or circum- 

 ferential lamina, parts of which have been removed by absorption. 



The circumferential laminae are not so constantly present as is 

 generally described, and rarely entirely surround the shaft of a long 

 bone. When present, they seem to indicate that the bone is nearly 

 stationary in its growth. They are frequently intersected by nume- 

 rous Haversian spaces and systems, so as at length to assume the 

 characters of interstitial laminae. 



3. LacuncE. — In 3'oungbone the lacuns are more abundant, larger, 

 and have more numerous canaliculi ; or they may exist without cana- 

 liculi, or the canaliculi and great part of the lacunae themselves may 

 be filled up with solid matter, so as to leave only a small space in the 

 centre of the latter, 'i'he lacuna and canaliculi are shown to have 

 distinct walls. 



