SECT. 89.] OSSEOUS SYSTEM. 1 67 



§ 89. Intimate Structure of the Osseous Tissue. — The osseous 

 tissue consists of a dense, for the most part indistinctly stratified 

 basal substance or matrix, penetrated by vascular canals, and of many 

 small microscopic spaces, the bone-cavities, lacuna? (bone-corpuscles 

 of authors), furnished with fine hollow processes, the canaliculi. 



The vascular canals of the bones, or the Haversian canals (me- 

 dullary canals of authors), are fine tubes, of an average breadth 

 of o'oi'" to 0'05'", but varying from o - oo4'" to cn8'", which, 

 except in the above-mentioned localities, are everywhere found in 

 the compact osseous substance, and form in it a network with 

 wide meshes, similar to that of the capillary vessels. In the 

 cylindrical bones, as also in the ribs, the clavicle, pubes, ischium, 

 and inferior maxilla, they run chiefly in a direction parallel to the 

 long axis of the bone ; and, in longitudinal sections, whether 

 parallel to the surface or perpendicular to it, appear at distances 

 of o , o6" to 0*14'" apart. They are connected with each other by 

 small branches running obliquely or transversely, as well in the 

 direction of the radius as that of the tangent of the transverse 

 section. Accordingly, in a longitudinal section parallel to the 

 surface, or perpendicular to it, there are seen, with a low magnifying 

 power, canals lying closely together, and principally longitudinal 

 and parallel to each other. Here and there, they are united by 

 connecting branches, so that elongated, and, for the most part, 

 rectangular meshes are formed, which, in the young osseous sub- 

 stance, are disposed much more closely than in the fully developed 

 layers. A transverse section shows chiefly transverse sections of 

 the canals at tolerably regular distances from each other (fig. 76), 

 and occasionally, especially in young bones, connecting branches 

 in a tangential direction, and some anastomoses radially. Foetal 

 and unfinished bones present, in cross sections, almost no trans- 

 versely cut canals (fig. 75), but chiefly such as run horizontally in 

 the direction of the tangent and radius, so that the bones appear 

 to be wholly composed of short thick layers, each of which, on 

 close examination, is found to belong to two canals, which relation 

 is also indicated by a faint line of separation in the middle of each 

 layer. In man, this condition is still observable in the eighteenth 

 year. 



In the flat bones, only a few of the canals run in the direction 

 of the thickness of the bone, their general course being parallel to 

 its surface, and mostly in lines which may be conceived to radiate 

 from a point (tuber parietale, frontale, upper anterior angle of the 

 scapula, articular part of the ilium) in a stellate manner towards 



