1 68 OSSEOUS SYSTEM. [sect. 90. 



the borders; more rarely, all parallel to one another, as in the 

 sternum. Lastly, in the short bones, one direction also prepon- 

 derates; thus, in the bodies of the vertebrae the prevailing di- 

 rection is perpendicular; in the carpus and tarsus, etc., it corre- 

 sponds with the long axis of the limb. It is, however, to be 

 observed, that the more considerable processes of these bones (for 

 example, those of the vertebrae) deviate from this condition, and 

 present the same arrangement as the short cylindrical bones, 

 which is the case, indeed, with similar processes of other bones, 

 such as the coracoid, styloid, etc. The laminae, fibres, and trabe- 

 cule of the spongy substance, when rather thick, contain here and 

 there vascular canals. As the Haversian canals contain blood- 

 vessels, they open at certain places, namely, upon the outer surface 

 of the bones, and on the walls of the medullary cavities and spaces 

 in the interior ; in all of which places smaller and larger pores are 

 perceived, which are, in part, visible to the naked eye, and are the 

 more numerous the thicker the cortex of the bone. The relation 

 of the vascular canals within the compact substance to those which 

 penetrate it from without, or at its inner boundary, can be compared 

 to that between the branches and trunks of vessels only in the outer- 

 most and innermost layers of the cortex. In the interior of the cortex, 

 the canals can, morphologically, be most aptly compared with a 

 capillary network, which, at its boundaries, stands in many places 

 in connection with larger canals. Where cortical substance adjoins 

 spongy substance, as within the extremities of the diaphyses and 

 in the lateral circumference of the apophyses, the vascular canals, 

 widening in an infundibuliform manner, sometimes suddenly, 

 sometimes gradually, and anastomosing more frequently, thus pass 

 into medullary spaces of various widths (Haversian spaces, Tomes 

 and Be Morgan), so that there is often no sharp line of demar- 

 cation visible between them. I have never yet seen blind termi- 

 nations of the vascular canals ; yet it is certain that, in many places, 

 and also upon the surface, they must form closed networks over a 

 considerable extent, viz., wherever very few or no vessels penetrate 

 into the compact substance, as at the places of attachment of many 

 tendons and ligaments, beneath many muscles, etc. (origin of the 

 temporal muscle from the parietal bone). 



§ 90. The substance of the bones is stratified, and the osseous 

 lamella? (fig. 76) come still more distinctly to view in bones de- 

 prived of their calcareous earths, or in such as have been exposed 

 to the weather or calcined ; in which cases the laminae exfoliate, 



