32-i THE TISSUES. 



Tomes and De Morgan (with Yirchow, and more recently Hoppe) 

 assert that the lacunae and pores have distinct walls, 1 as is the case 

 with the dentinal tubuli. Like the latter, they are also sometimes 

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

 centre. These observers also found a modification of the lacunae 

 in the circumferential laminae of bones; they there being elongated 

 tubes, and passing, in bundles or singly, more or less obliquely, 

 from the surface towards the interior of the bone. The largest are 

 sometimes bent once or twice at a sharp angle. They have distinct 

 walls, and are connected laterally with the pores. 



The contents of the lacunae are first, a nucleus ; and, secondly, a 

 clear fluid ; thus resembling the contents of cartilage -cavities. (Kol- 

 liker.) Their relation to the cartilage-cells will be explained under 

 the head of "Development of Bone." The fluid is doubtless the 

 nutritive fluid of the bone, and is therefore plasma, or a modifica- 

 tion of it. 



The lacunae and pores do not present precisely the same condi- 

 tions in the compact and the cancellated substance of bone, as will 

 be shown (pp. 328 and 330). 



2. The Vascular Canals of Osseous Tissue. 



The vascular or Haversian canals are minute tubular passages 

 in the bone-substance, averaging J^OF to sio f an i nc h ( tne e3> 

 tremes being -g oW an d g^) ; and which exist everywhere in the 

 compact bone-substance, except in the thinnest layers of it, forming 

 a network similar to that of the capillaries in the soft tissues. 



In the long bones, and in the ribs, clavicle, os pubis, and ischium, 

 they chiefly run parallel to the long axis of the bone ; and almost 

 always either parallel to the surface, or perpendicular to it, and from 

 2&tf to sV f an i ncn a P art - These are, however, connected by 

 transverse or oblique branches. Thus they form a network con- 

 sisting of elongated and generally rectangular meshes, as seen in 

 the longitudinal section of a long bone, Fig. 214. Few transverse 

 communicating canals occur, however, in foetal and still undeveloped 

 bones. 



In the flat bones, almost all the Haversian canals run parallel to 

 their surface, and sometimes, indeed, in lines radiating from one 

 point (as the parietal protuberance, upper and anterior angle of the 



1 Lehmann infers, also, from Hoppe's experiments, that the lacunae and pores are 

 lined by an albuminous membrane, insoluble in boiling water. 



