302 SPECIAL HISTOLOGY. 



directions, their course being irregular, and often actually 

 curved. They proceed principally, however, in the first place, 

 from both surfaces of the lacunas straight through the 

 lamellae ; and secondly, parallel with the Haversian canals, from 

 the two poles of the lacunas. It is only in certain limited spots 

 that these canaliculi present ccecal terminations; everywhere 

 else some of them anastomose in the most various wavs with the 

 canaliculi of the neighbouring lacunae, whilst others commu- 

 nicate with the vascular canals, the medullary cavities, and the 

 medullary spaces or cancelli of the spongy substance, or open 

 on the surface of the bone. The entire osseous substance, there- 

 fore, is penetrated by a connected system of cavities and canaliculi , 

 „. ,,, bv means of which the nu- 



Fig. 11G. 



at, c , tritive iuice secreted bv the 



vessels is conveyed into its 



-• ' ' densest tissue. 



W[ r v-. The lacunas and canaliculi 



s do not exhibit precisely the 



• m same conditions in every 



part of the bones. In the 



*■- lamellar systems of the 

 %'-, .?'. Haversian canals, as seen 



afe w 



in a transverse section, the 



pp elongated lacuna?, by reason 



Tpr ? ,'/, •': _ of their curvature, lie as it 



1 V were concentric to the canal, 



l?~? and their excessively nuine- 



^ -■■' rous pores or canaliculi ne- 



x . 



cessarily produce a very close 



striation radiating from the 



: ' t'' 1 , j vascular canal (fig-. 115). 



The lacunas are sometimes 



extremely numerous, some- 



times more scantv; in the 



former case they are, for the most part, arranged in tolerably 



regular alternation, or one behind the other in the direction of 



Fig. 116. Section parallel with the surface from the shaft of a human femur, 

 x 100 diam.: a, vascular canals ; b, lacunae seen from the side, belonging to the 

 lamellae of these canals; c, lacuna? viewed on the flat side, in lamella; which are cut 

 horizontally. 



