THE OSSEOUS SYSTEM. ~ H .>7 



between the other lamella? (fig. 112, d). In the interior of the 

 compact substance, on the other hand, in man, the Haversian 

 systems are so closely crowded, that there can be no question 

 as to the non-existence of lamellar groups between them, and 

 it is evident that those lamelhc, which in a transverse section 

 appear in man to be parallel with the surface, almost all belong 

 to horizontal canals : and it is but rarely that distinct inter- 

 stitial masses are seen, as is usuallv the case in other main- 

 malia. The thickness of the separate lamelhc just described 

 is much the same as that of the lamellae of the Haversian 

 canals, and their number varies from 10 to 100. 



VCe have hitherto considered only the diaphyses of the long 

 bones. In their apophyses, the thin cortical layer of compact 

 substance naturally presents only a few systems of Haversian 

 canals, which, however, are constituted as elsewhere. The 

 exterior fundamental lamella? are few in number, and inter- 

 nally, owing to the existence there of the spongy substance, 

 they are wholly wanting. In the latter substance, the very 

 few Haversian canals present lamellar systems as usual, except 

 that they are thin, and the remainder, according to the con- 

 dition of the osseous network, consists of a lainellated and 

 fibrous tissue, which in general follows the contour of the 

 medullary spaces and cells. The flat and short bones present 

 a similar arrangement internally, whilst the cortical substance 

 of these bones differs from that of the cylindrical, only in the 

 circumstance, that the fundamental lamella?, in the flat bones, 

 form layers parallel with both surfaces of the bone. The 

 thickness of the fundamental lamellae in the cranial bones 

 (parietal), is sometimes the same in both aspects, and varies 

 from 0-08'" to 0-16'", sometimes thev are wanting in vascular 

 situations, and in places, wholly so, on the external aspect of 

 the bone, in which case the Haversian lamella? reach almost to 

 the surface. 



With respect to the intimate structure of the osseous lamella?, 

 which is best studied in transverse sections, dried, polished, 

 and sufficiently thin, there is usually evident, besides the bone- 

 cells and canaliculi, in the generally not very distinct lamella?, 

 an extremely fine though very distinct punctated appearance, 

 so that the whole osseous tissue appears granular, and to be 

 composed as it were of separate, densely crowded, pale granules, 



