228 .CONNECTIVE TISSUE. 



The center of the Haversian system is pierced by the medul- 

 lary or vascular canal, which is of a varying caliber, according to 

 the age of the individual, and contains, besides a certain number 

 of medullary corpuscles, one or two central capillary blood- 

 vessels. Whenever the extremity of the animal from which the 

 shaft-bone was taken had been in a pendent position after death, 

 the vessels are found filled with blood-corpuscles. 



Longitudinal Sections are easily understood after the study of 

 transverse sections. Here, too, the Haversian system is bordered 

 by a fluting contour, due to the presence of globular territories of 

 an early formation, and between the systems we find the inter- 

 mediate bone-tissue, which in this situation, as a matter of 

 course, will not exhibit lamination. In the intermediate portion 

 we find the bone-corpuscles cut transversely, with most of their 

 offshoots cut either obliquely or transversely, the latter being 

 represented by a number of delicate dots. 



In the Haversian system the lamellae take a longitudinal 

 course ; within and between them are found the spindle-shaped 

 bone-corpuscles, exhibiting, for reasons explained before, the 

 greater bulk the nearer the periphery of the system. The off- 

 shoots of the bone-corpuscles emanating from their periphery, as 

 well as from their polar projections, pierce the lamellae at right 

 angles. The central canal contains a varying number of medul- 

 lary corpuscles, and in its middle one or two straight capillaries. 

 Even with moderate powers of the microscope delicate filaments 

 are recognizable, by which the offshoots of the bone-corpuscles 

 connect with the medullary corpuscles, and the latter with the 

 endothelial wall of the blood-vessel. (See Fig. 89.) 



Periosteum. The investing fibrous connective-tissue layer of 

 all bones, the periosteum as well as the cartilage, takes consid- 

 erable part in the development of the osseous system. In human 

 embryos of four to six months, the outermost layer of the peri- 

 osteum consists of bundles of fibrous connective tissue, and 

 between this layer and the cancellous bone there is a broad layer 

 of medullary corpuscles, in continuity with the medullary forma- 

 tion in the spaces of the bone-tissue. From the outer fibrous 

 portion of the periosteum oblique bundles of considerable density 

 are seen to pass into the medullary spaces of the bone, and these 

 bundles remain unchanged even after the compact portions of 

 the bone have attained full development. Such bundles, faintly 

 visible in chromic acid specimens, .are termed " perforating or 

 Sharpey's fibers" (described by Sharpey in 1856, but previously 



