202 



SPECIAL HISTOLOGY. 





tions of one of those bones, either parallel to the surface or 

 perpendicular to it, closely approximated canals running parallel 

 to each other, chiefly in a longitudinal direction, are seen, here 

 and there with connecting branches, and thus forming a net- 

 work, consisting of elongated, and most generally, rectangular 

 meshes (fig. 111). And in a transverse section — transverse sec- 

 tions of the canals, placed at 

 tolerably definite but small dis- 



tances apart, are principally ap- 

 parent (fig. 112); which, more 

 especially in younger bones, 

 are occasionally connected by 

 a tangential branch, and some 

 anastomoses in the direction 

 of the radius. In transverse 

 sections of foetal and unde- 

 veloped bone (in man even at 

 the age of eighteen), scarcely any transverse canals occur, but 

 chiefly those running horizontally in the direction of the 

 tangents and radius (fig. 110), so that the bones appear to 

 consist entirely of short thick lamellae, each of which, upon 

 closer examination, is seen to belong to two canals, and exhibits 

 a pale central line, indicating the division between the two con- 

 stituent portions of which it is formed. 



In the flat bones, the greater number of the canals do not 

 run in the direction of the thickness of the bone, but almost 

 all, parallel with its surface, and indeed in lines which may 

 be conceived as radiating from one point [tuber parietale, 

 frontah, upper and anterior angle of the scapula, articular 

 portion of the ilium) in a penicillar or stellate manner towards 

 one or several sides ; or less frequently, as in the sternum, are 

 all parallel to each other. In the short bones, lastly, there is 

 most usually one predominant direction in which the canals 

 run, as the vertical in the vertebrae, — that of the long axis of 

 the extremity in the carpal and tarsal bones, &c. ; it must be 

 remarked, however, that the larger processes of these bones, 

 as, for instance, the spinous processes of the vertebrae, differ in 



Fig. 111. Haversian canals from the superficial lamella; of the y«Mwr of an indi- 

 vidual 18 years old, treated with hydrochloric acid, x 60 diam.: a, canals; b, osseous 

 substance with lacunae. 



