

COMPOSITION OF BONE. 179 



phosphates ; one atom of the neutral phosphate (in which one propor- 

 tional of the a,cid is united with two of lime and one of water), being 

 united with two proportionals of the alkaline phosphate (in which one 

 part of acid is united with three of the base), together with an atom of 

 water, which is driven off by calcination. Besides these components, 

 some Chemists assert that a small quantity of Fluoride of calcium is 

 present in Bone ; but this is rather doubtful, since it has been shown 

 by Dr. Gr. 0. Rees that the solvent action upon glass, which has been 

 supposed to be characteristic of fluoric acid, may be imitated by phos- 

 phoric acid in combination with water, which, if heated upon glass of 

 inferior quality until it volatilizes, will act upon it with considerable 

 energy. Other saline matters, such as phosphate of magnesia, oxides 

 of iron and manganese, and chloride of sodium, are found in bones in 

 small amount. 



300. The first development of Bone is usually preceded by the for- 

 mation of a Cartilaginous structure, which occupies the place after- 

 wards- to be taken<by the bone; and it is commonly considered that the 

 bone is formed by the calcification of the cartilage-substance. This, 

 however, does not appear to be the case, as will be presently shown ; 

 and it would probably be more correct to say that the cartilage is super- 

 seded by bone. Moreover, Bone is frequently developed in the sub- 

 stance of Fibrous membranes ; and the structure produced by this intra- 

 membranous ossification cannot be distinguished from that which is 

 generated by the intra-cartilaginous. We shall commence the history 

 of the development of Bone, with the period in which its condition 

 resembles that of the permanent Cartilages. As already mentioned, 

 there is no essential difference between the temporary and permanent 

 Cartilages, in regard to their ultimate structure ; the former, however, 

 are more commonly traversed by vessels, especially when their mass is 

 considerable. These vessels, however, do not pass at once from the 

 exterior of the cartilage into its substance ; but they are conveyed in- 

 wards along canals, which are lined by an extension of the perichondrium 

 or investing membrane, and which may thus be regarded as so many 

 involutions of the outer surface of the cartilage. These canals are espe- 

 cially developed at certain points, which are to be the centres of the 

 ossifying process; of these puncta ossificationis, we usually find one in 

 the centre of the shaft of a long bone, and one in each of its epiphyses ; 

 in the flat bones there is one in the middle of the surface, and one in 

 each of the principal processes. Up to a late /stage of the ossifying 

 process, the parts which contain distinct centres are not connected by 

 bony union, so that they fall apart by maceration; and even when they 

 should normally unite, they sometimes remain separate, as in the case 

 of the Frontal bone, in which we frequently meet with a continuation 

 of the sagittal-suture r"own the middle, dividing it into two equal halves, 

 which have originated in two distinct centres of ossification. It is inte- 

 resting to remark that, in the two lowest classes of Vertebrata, Fishes 

 and Reptiles, we find the several parts of the osseous system present- 

 ing, in a permanent form, many of the conditions which are transitory 

 in the higher ; thus the different portions of each vertebra, the body, 

 lateral arches, spinous and transverse processes, &c., which have their 



