4fi8 Roynl Societij. 



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 

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

 have been encroached on by the process of absorption. 



In examining various sections, or different parts of the same 

 section, many of these spaces will be found which have become par- 

 tially or entireljr occupied by Haversian systems. They are fouird 

 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. Lamince of bone. — 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 ^^.rt. 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 arc regular in outline. 



The lamince 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 more are deve- 

 loped on one side than on the other. The lamina next to the per- 

 fected 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 

 circumferential laminae, parts of which have been removed by 

 absorption. 



The circumferential laminae are not so constantly pi-esent as is 

 generally described, and seldom 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 lamina?. 



3. Lacunas. — In young bone the lacunre are more al)undant, larger, 

 and have more numerous canaliculi ; in older bone they may exist 

 without canaliculi, or the canaliculi and great part of the lacunau 

 themselves may be filled up with solid matter, so as to leave only a 

 small space in the centre of the latter. The lacunai! and canaliculi 

 are shown to have distinct walls. 



In the circumferential laminae are frequently found elongated tubes 

 Avhich 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 projier 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 



