282 OF THE PRIMARY TISSUES OF THE HUMAN BODY. 



through, and the extremities have been brought evenly together, it is found that 

 the new matter first ossified is that which occupies the central portion of the 

 deposit, and which thus connects the medullary cavities of the broken ends, 

 forming a kind of plug that enters each. This was termed by Dupuytren, by 

 whom it was first distinctly described, the provisional callus ; and it serves to 

 hold the bones together during the formation of the permanent callus, which passes 

 directly between the fractured surfaces, and which usually requires a much longer 

 time for its production. After this more direct union has been established, the 

 provisional callus is gradually absorbed, and the continuity of the medullary 

 canal is thus restored, in the manner in which it was first established. These 

 statements do not apply to Man, however, without great modification. For, as 

 Mr. Paget has pointed out, 1 it is very rare to find a true provisional callus unit- 

 ing the fractured ends of a human bone ; and since, where this does present 

 itself, as in the ribs, and occasionally in the clavicle, the two broken ends are in 

 a state of continual movement, we are probably to attribute its absence in other 

 cases to the maintenance of quietude and more perfect apposition. Mr. Gulli- 

 ver has remarked 2 that, when the broken portions of bone form an angle, there 

 is quite a distinct centre of ossification in the new matter, from which that por- 

 tion of it is ossified, that lies between the sides of the angle ; thus forming what 

 has been termed an accidental callus, and giving support to the two portions 

 of the shaft, in a situation which is exactly that of the greatest mechanical 

 advantage. Though for some time quite unconnected with the old bone, it soon 

 becomes united to the regular callus. This instance proves, that continuity with 

 previously-formed bone is not absolutely requisite for the production of new 

 osseous structure ; although the process is decidedly favored thereby. 



273. The production of new Osseous tissue, after disease or injury, seems 

 to take place upon a plan essentially the same as its original formation. A 

 plastic or organizable exudation is first poured out from the neighboring blood- 

 vessels ; and this nucleated blastema may itself, according to Mr. Paget's observ- 

 ations, 3 undergo conversion into bone, without any intermediate stage ; a 

 finely-granular osseous deposit taking place in the blastema, and gradually accu- 

 mulating so as to form the delicate yet dense lamellae of fine cancellous tissue ; 

 and the nuclei apparently giving origin to the osseous lacunse and canaliculi. 

 But where this simplest form of the process does not take place, the nucleated 

 blastema gives origin either to a cartilaginous or to a fibrous structure, or to a 

 combination of both. The former seems more common among the lower animals, 

 especially when they are young, than it is in Man ; when it occurs, the cartilage 

 is converted into bone after the usual manner. In older animals, however, the 

 new structure appears to be rather of a fibrous character ; and the ossifying pro- 

 cess would therefore correspond rather with that, by which the normal increase 

 of their bones is effected. Mr. Tomes states 4 that he has examined various cases 

 of fracture of the neck or shaft of the femur, in which union has not been 

 effected, in consequence of the patient's advanced age; and that he found in 

 these no intervening cartilage, and but a scanty amount of condensed areolar 

 tissue. In this latter, traces of an attempt at repair may be generally found, in 

 the presence of osseous matter in granules or granular masses ; but in these there 

 is no arrangement of tubes or bones-cells of definite character; indeed, such 

 osseous masses are generally small, and are deficient in density, owing to the 

 want of union between the individual granules. 



274. The Teeth are nearly allied to Bone in structure; and in some of the 



1 "Lectures on Repair and Reproduction," in "Medical Gazette," July 20, 1849, p. 

 116. 



2 "Edinb. Med. and Surg. Journal," vol. xlvi. p. 313. 

 9 Op. cit, pp. 120, 121. 



"Cyclopsedia of Anatomy and Physiology," vol. iii. p. 857. 



