OSSEOUS TISSUE. 115 



vertebrge and pelvis. It is rare for true bones and uncalcified 

 cartilage to enter into direct contact with one another. 



Calcification also occurs in cartilages which, like those of the 

 larynx, begin to ossify with advancing age. In such cartilages 

 it often happens that, notwithstanding parts are found in which 

 both to the eye and touch earthy matters appear to be deposited, 

 examination with the microscope reveals the presence of no 

 true bone, but only of calcified cartilage. Reticulated cartilage 

 only calcifies exceptionally in certain animals, as in the dog* 



OSSEOUS TISSUE. 



Osseous tissue forms in man the principal constituent of the 

 bones of the skeleton, and of the cementum of the teeth. This 

 is equally true of all Vertebrate animals. A number of osseous 

 fishes, however, instead of having their skeleton composed of 

 true bone, present a homogeneous or fibrous osteoid substance, 

 traversed by dentine-like tubes which may become actual den- 

 tine.^ Taking the vertebrate series as a whole, the osseous tissue 

 is widely distributed, since certain parts which are elsewhere 

 composed of soft tissues, as the skin, tendons, and sclerotic 

 coat of the eye, in some animals contain bone. In man, also, 

 osseous tissue occurs in some soft parts as a pathological 

 formation. 



STRUCTURE OF OSSEOUS TISSUE. In a histological point of 

 view, we distinguish in the first place in osseous tissue the 

 matrix and the bone corpuscles. The distinction between these 

 two constituents of bone may be easily perceived on microscopic 

 examination, by transmitted light, of the frequently well-deve- 

 loped thin osseous plates that occur in pathological ossifications, 

 or of the laminse of the vomer, lachrymal bones, etc., or of fine 

 sections prepared from the larger bones. The corpuscles appear 

 as dark black figures, which consist of a central area,, which is 



* H. Miiller, Wiirzburg naturwissenschaftliche Zeitschrift, Band i., p. 92. 



t Koliiker, Ueber verschiedene Typen in der Mikroskopischen Structur 

 des Skelettes der Knochenfische, " On the various Types of Microscopic 

 Structure in the Skeleton of Osseous Fishes." Aus dem ix. Bande der 

 Wurzburger Verhandlungen. 



