HUMAN ANATOMY. 



BONE OR OSSEOUS TISSUE. 



In the higher vertebrates, osseous tissue forms the bony framework, or skeleton, 

 which gives attachment and support to the soft parts, affords protection to the more 

 or less completely surrounded delicate organs, supplies the passive levers for the 

 exercise of muscular action, insures stability, and maintains the definite form of the 

 animal. 



In addition to contributing the individual bones composing the principal, and 

 in man the only, framework, or entoskeleton, osseous tissue occurs in the lower ver- 

 tebrates associated with the integument as an exoskeleton. Representatives of the 

 latter are seen in the bony plates present in the skin of certain ganoid fishes, 

 the dermal plates of crocodiles, the dorsal and ventral shields of turtles, or the 

 dermal armor of the armadillo. Osseous tissue also exists within various organs in 

 certain animals and then constitutes the splanchnoskeletoyi. Examples of the latter 

 are furnished by the bony plates encountered in the sclerotic coat of the eyes of 

 birds, in the diaphragmatic muscle of the camel, in the tongue of certain birds, in 

 the heart of ruminants, in the nose, as the snout-bones of the hog, in the respiratory 

 organs, as the laryngeal, tracheal, and bronchial bones of birds, and in the genital 

 organs, as the penile bone of carnivorous and certain other mammals. 



True osseous tissue does not occur outside the vertebrates. Many invertebrate 

 animals possess a skeletal framework, usually external but in some cases internal. 

 Such a framework, however, consists of calcareous incrustations, hardened excre- 

 tions or concretions composed principally of calcium carbonate and of silicious 

 structures. These earthy or mineral hard parts of invertebrates are structureless 

 deposits, so differing materially from the bone tissue of the higher vertebrates as 

 well in structure as in chemical composition. Sometimes a deposit of calcareous 

 material occurs in adult cartilage, a process entirely distinct from the formation of 

 bone tissue. Familiar examples of such calcification are seen in the costal and some 

 of the laryngeal cartilages. 



Chemical Composition. — Bone is a dense form of connective tissue, the 

 matrix of which is impregnated with lime salts ; it consists, therefore, of two parts, 

 an anhnal and an earthy portion, the former giving toughness and the latter hardness 

 to the osseous tissue. 



The animal or organic part of bone may be removed by calcination, leaving the 

 inorganic constituents undisturbed. If a bone be heated in a flame with free access 

 of air, the animal matter at first becomes charred and the bone black ; continued 

 combustion entirely removes the organic materials, the earthy portion alone remain- 

 ing. After such treatment, while retaining its general form, the bone is fragile and 

 easily crushed, and has suffered a loss of one-third of its weight, due to the destruc- 

 tion and elimination of the animal constituents. The latter, evidently, constitute 

 one-third and the mineral matters two-thirds of the bone. The inorganic constitu- 

 ents include a large amount of calcium phosphate, much less calcium carbonate, with 

 small proportions of calcium fluoride and chloride, and of the salts of magnesium and 

 sodium. 



The animal portion of the bone, on the other hand, may be separated from the 

 inorganic salts by the action of dilute hydrochloric acid, which dissolves out the 

 earthly constitutents ; after such treatment the bone, although retaining perfectly 

 its form and details, is tough and flexible, a decalcified rib or fibula being readily 

 tied into a knot. The animal constituents of bone yield gelatin upon prolonged 

 boiling in water, therein resembling fibrous connective tissue. 



The composition of bone, according to Berzelius, is as follows : 



Organic matter Gelatin and blood-vessels, 



f Calcium phosphate, 



I Calcium carbonate. 



Inorganic matter •• • i Calcium fluoride. 



Magnesium phosphate, 



. Sodium oxide and sodium chloride, 



