STRUCTURE OF BONE. 



bring on collapse, deprive him of breath for some time, and leave him gasping and 

 speechless on the ground ; while a tolerably severe blow in that region causes instan- 

 taneous death. 



Anxiety seems to fix its gnawing teeth chiefly in the solar plexus, causing indigestion 

 and many other similar maladies, and deranging the system so thoroughly that even after 

 the exciting cause is removed the effects are painfully evident for many a sad 

 year. 



By means of this complicated system of nerves the entire body, with its vital organs, 

 is permeated in every part by the animating power that gives vitality and energy to the 

 frame so long as the spirit abides therein. 



This is the portion of the nervous system that never slumbers nor sleeps, knowing 

 no rest, and never ceasing from its labors until the time comes when the spirit finally 

 withdraws from the material temple in which it has been enshrined. It is the very 

 citadel of the nerve forces, and is the last stronghold that yields to the conquering 

 powers of death and decay. 



Thus it will be seen that each animal is a complex of many animals, interwoven with 

 each other, and mutually aiding each other, In the human body there is, for example, 

 the ne*ve-man which has just been described ; there is a blood-man, which, if separated 

 from the other part of the body, is found to present a human form, perfect in propor- 

 tions, and composed of large trunk-vessels, dividing into smaller branches, until they 

 terminate in their capillaries. A rough preparation of the blood-being may be made by 

 filling the vessels with wax, and dissolving away the remaining substances, thus leaving 

 a waxen model of the arteries and veins with their larger capillaries. 



Again, there is the fibrous and muscular man, composed of forms more massive and 

 solid than those which we have already examined. 



Lastly, there is the bone-man, which is the least developed of the human images, 

 and which, when stripped of the softer coverings, stands dense, dry, and lifeless ; the 

 grim scaffolding of the human edifice. Although the bones are not in themselves very 

 pleasing objects, yet their mode of arrangement, their adaptation to the wants of the 

 animal whose frame they support, and the beau- 

 tiful mechanism of their construction, as revealed 

 by the microscope, give a spirit and a life, even to 

 the study of dry bones. 



The accompanying illustration represents the 

 appearance of a transverse section of human 

 bone,as seen under a tolerably powerful micro- 

 scope. 



The larger hollows are caused by the minute 

 blood-vessels which penetrate the bone through- 

 out its substance, and serve to deposit new par- 

 ticles, and to remove those whose work is over. 

 They are, in fact, a kind of lungs of the bones, 



SECTION OF HUMAN BONE. 



through which the osseous system is regenerated in a manner analogous to the respira- 

 tion which regenerates the blood. In order to supply a sufficient volume of blood to 

 these various vessels, several trunk vessels enter the bones at different parts of their 

 form, and ramify out into innumerable branchlets, which again separate into the hair- 

 like vessels that pass through the above-mentioned canals. These are termed, from 

 their discoverer, C. Havers, the Haversian canals, and their shape and comparative 

 size are most important in determining the class of beings which furnish the portion 

 of bone under examination. 



In the human bone these canals run so uniformly, that their cut diameters always 

 afford a roundish outline. But in the bird-bone, the Haversian canals frequently turn 

 off abruptly from their course, and running for a short distance at right angles, again 

 dip and resume their former direction. 



The reptiles possess very few Haversian canals, which when they exist, are extremely 

 large, and devoid of that beautiful regularity which is so conspicuous in the mammalia, 

 and to a degree in the birds. 



