THE OSSEOUS SYSTEM. 



303 



the radius of the lamellar system; but they arc also frequently 

 disposed very irregularly, either crowded together {vide the 

 lower part of fig. 115), or separated by wider interspaces. In 

 horizontal and longitudinal sections of Haversian canals 

 (fig. 116), when the section has passed through the middle of a 

 canal, the lacuna; appear narrow and elongated, and disposed 

 in rows one behind the other, and in numerous layers parallel 

 with the canal; and also furnished with numerous canaliculi, 

 which proceed for the most part directly inwards and outwards 

 (consequently transversely through the lamellae), but partly in a 

 direction parallel with the long axis of the canal. If the section 

 strike the surface of a system, the superficial lacunae come 

 into view, presenting very elegant forms, rounded or oval 

 (figs. 115 d, and 117), surrounded in an irregular manner by a 



Fie. 117. 



complete tuft of canaliculi, which look directly towards the 

 observer, and consequently appear more or less shortened, and 

 by a smaller number of other canaliculi distributed on the 

 surface of the lamellae. Occasionally, even in the thinnest 

 parts of a section, there occurs a tuft of canaliculi, cut across 

 transversely, and without the lacuna to which they belong, 

 whence these portions of bone exhibit a sievelikc aspect. All 



Fig. 117. Lacunse viewed on the flat side, with the canaliculi, from the parietal 

 bone, x 450 diam. The spots on the lacunas or between them belong to canaliculi, 

 which are cut across, or are the openings of canaliculi into the lacunae ; aaa, groups 

 of transverse sections of canaliculi, each group belonging to a lacuna which has been 

 destroyed in the making of the section. 



