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DEVELOPMENT OF BONES. 



Bones, before arriving at tho state in which they present themselves in 

 the adult animal, pass through several successive phases, whoso study consti- 

 tutes what is termed odeogeny. 



In the embryo, at a very early period, the bones are composed of a 

 mucous material analogous to that which enters into the composition of all 

 tho other organs; this matter is constituted by amass of what arc called 

 embryonic cells. At a later period they are impregnated with gelatine, and 

 nearly all become harder, white, and elastic, passing into the cartilaginous 

 state. Exception must bo made, however, to the lateral and anterior pari< ti s 

 of the cranium and the face, tho bones of which are at first fibrous but 

 never cartilaginous. The cartilaginous bones show a fundamental amorphous 

 substance, in which are disseminated spherical cells containing one or more 

 nuclei. This condition is transitory ; the cartilaginous tissue soon submits 

 to modifications which result in conferring on the pieces that it composes 

 the hardness and structure of perfect osseous tissue. These modifications 

 constitute the process of ossification. There are several portions of tho 

 skeleton which do not undergo this osseous transformation, and which 

 most frequently remain in the cartilaginous condition during the entire lifo 

 of the animal. These permanent cartilages are met with at those points 

 where the bony skeleton must preserve a certain degree of flexibility, 

 and on the articular surfaces. During the process of ossification, tho 

 cartilages become vascular, are impregnated with calcareous salts, and 

 excavated with Haversian canaliculi and medullary cavities. The saline 

 molecules are deposited in the amorphous substance, which grows more 

 hard and opaque ; at the same time the cartilaginous cells become the point of 

 departure of a new embryonic proliferation, from which results the ncoplasts. 



Ossification begins at the same time in several parts of the skeleton, and 

 in each of the bones in particular ; though it does not appear over the 

 whole extent of the latter at once; on the contrary, in certain determinate 

 points of the cartilaginous mass, bony tissue can be perceived developing 

 itself and extending gradually until it finishes by completely invading it. 

 These points are called centres of ossification. 



These centres are primary or complementary ; the latter are in some way 

 added to the bone, and form, wholly or in part, certain processes. Although 

 these centres of ossification enlarge from day to day, yet for a somewhat 

 long period they remain completely independent of one another, and are only 

 connected by cartilaginous tissue. 



The term epipliyses is given -to the osseous centres which are placed at 

 the extremities of the principal centre. When tho skeleton is completely 

 developed, the various centres of ossification are fused into each other, and 

 then there are no longer epiphyses ; this fusion always takes place at an almost 

 determinate epoch. It has been remarked that, of two epiphyses, it is con- 

 stantly the one near which tho nutritious foramen is directed that is first 

 united to the body of the bone. 



Growth. Bones grow in width and thickness by tho apposition of new 

 elements. In the long bones, tho growth in length takes place by the 

 ossification of the cartilage uniting the epiphyscs to the body of the bone. 

 Consequently, elongation should cease as soon as the epiphyses are ineor- 

 porated with the diaphysis. With regard to the long bones of tho limbs, 

 JJuliamol, Flourens, and particularly MM. Oilier and Humphry, Jiavo 

 remarked that, in the thoracic limb, the extremity furthest removed from 



