BONE. 45 



is a free growth of corpuscles (termed osteoblastic) and blood- 

 vessels. Whether the corpuscles are derived from those of 

 the cartilage, or from the connective tissue round the vessels, 

 is not settled ; but they become imbedded in a new deposi- 

 tion of calcified matrix, which leaves them, with freely in- 

 tercommunicating branches, and are thus converted into true 

 bone-corpuscles. 



The first deposit of bone is dense and irregular : if the 

 spaces formed in this by absorption accumulate, cancellated 

 tissue is the result ; but if they become filled with a new 

 deposit of bone, this deposit takes place in concentric rings, 

 gradually closing round the blood-vessels, and compact tissue 

 is produced. 



In cancellated, as well as in compact tissue, there is con- 

 tinual deposit and reabsorption of bone; but in the compact 

 tissue, the osseous substance is in such proportion to the vas- 

 cular, as to surround the vessels; while in the cancellated, 

 the vascular connective tissue, or red marrow, is in such 

 quantity as to surround the osseous spicules. 



When bone is developed from fibrous tissue, there is no 

 granular stage in ossification; but bony tissue is laid down at 

 once, as in spaces formed by absorption. 



24. While cartilage is capable of rapid growth, as has been 

 already stated, by multiplication of its corpuscles and expan- 

 sion of its matrix, bony tissue is capable of very little ex- 

 pansion, and increases in bulk by addition to its surfaces, 

 where it is in contact with cartilage or fibrous tissue. Thus, 

 a ring of silver fastened round the wing-bone of a young 

 pigeon becomes gradually imbedded and covered in by the 

 new depositions of bone on the surface, while, by the absorp- 

 tion which is at the same time going on internally, it may 

 even come to lie in the enlarged cavity of the bone. John 

 Hunter found, that if two holes were bored in a bone of a 

 young animal, at a measured distance one from the other, 

 afterwards when the bone had grown longer, the holes remained 

 separated by the same interval as at first. Even apart, how- 

 ever, from the circumstance that subsequent observers on 

 repeating Hunter's experiment have obtained a different 

 result, it must be admitted that osseous tissue has some 

 power, although limited, of interstitial expansion, seeing that 



