DEVELOPMENT OF BONE. 15^ 



Articular eminences. — A caput or head is a more or less semi- 

 >herical projection, supported by a roughened and constricted 



'vix or neck. An ovoid convexity is called a condyle; and 

 ften condyles are found in pairs, the articular surfaces of 

 which may be continuous or separated. A trochlea is an^ 

 articular surface presenting a pulley-like appearance. 

 ^^^ Articular depressions. — A glenoid cavity is shallow, and may 

 be cup-like, vt^hile a cavity is called cotyloid when it is deeper. 

 The term facet is often applied to articular surfaces, which may be 

 large, but are not well marked either as elevations or depressions. 



The rough irregularities of surface are more distinctly marked 

 in the bones of the horse than in those of most other animals; 

 their size is always proportionally greater in well-bred animals ; 

 in heavy, coarsely-bred horses, which possess great strength but 

 little activity, they are smaller in proportion to the absolute size 

 of the bones. 



DEVELOPMENT OF BONE. 



Although the bones of the foal, calf, and young of many other 

 large quadrupeds, possess greater solidity at birth than those of 

 the human infant, yet they all pass through certain progressive 

 stages of development before arriving at that degree of density 

 which they ultimately possess. The tracing of future bone is 

 recognised, about the seventh week of fcetal development, in local 

 collections of soft, granular, gelatinous pulp, which becomes 

 gradually flooded with nucleated cells, held together by an opaque, 

 intercellular basis or matrix, which, with the cells equally dis- 

 tributed through it, forms temporary cartilage — a material closely 

 resembling in its properties ordinary gristle. 



The process of ossification, or conversion of cartilage into bone, 

 begins at certain fixed points, and gradually spreads ; these points 

 are called ossific centres, or points of ossification. When this 

 conversion commeAces, that part of the cartilage about to become . 

 ossified is permeated by large channels for the passage of the 

 blood-vessels which convey the bone-earth ; and the cells, instead 

 of being equally distributed throughout the matrix, become 

 arranged in parallel groups, and increase in number, those nearest 



. the point of ossification enlarging. Matter, in the form of very 

 minute granules, is now deposited in this column of intercellular 



or hyaline substance, as well as between each cell. 



Ossification of the cell walls ensues, which is followed by the 



absorption of the osseous matter between the cells, converting 



what was a row of closed cells into a tube, which is a rudiment- 



