124 LOCOMOTION. [CHAP. v. 



around which the cancelli are very open, large,, and irregular. This 

 augmentation of the vascular cavities of bone is attended with a 

 development of adipose vesicles and their capillaries in the new 

 space, while the proper vessels of the osseous tissue remain pretty 

 much as before. The fat contained in the medullary canal gradu- 

 ally accumulates so much, that a special artery becomes enlarged to 

 supply it, assuming the very inappropriate title of " the nutrient 

 artery of the bone." Duhamel placed a ring of silver round a bone 

 of a young pigeon, without injuring the periosteum. After some 

 time, during which the bone had increased in diameter, he found 

 the ring in the medullary canal, which had acquired a capacity 

 equal to the previous diameter of the whole shaft. 



This enlargement of the diameter of a long bone by the dilata- 

 tion of its interior, is attended by two consequences, equally im- 

 portant. The shell of compact tissue is thus adapted to offer 

 greater resistance to injurious mechanical forces, while the dis- 

 advantage of a corresponding increase of weight is obviated. 



Reparation of Bone. The great importance of this subject to the 

 surgeon has led to many very interesting researches from the time 

 of Duhamel to the present day, and by these the several steps of 

 the process by which new bone is deposited have been ably eluci- 

 dated in all that relates to their more obvious characters. When 

 a fracture occurs, blood is, of course, effused into the wound, both 

 from the ruptured vessels of the bone itself, and from those of the 

 surrounding structures participating in the injury. At a short 

 period subsequently, a semi-transparent lymph is found mingled 

 with the coagulum, and covering the surfaces of the hard and 

 soft parts exposed. This lymph in all probability is the same as 

 that by which the adhesive process in other wounds is effected. In 

 the second and third weeks a gradual condensation of this takes 

 place, accompanied with an interstitial change, converting it into a 

 substance resembling temporary cartilage. 



Ossification takes place throughout this in a nearly uniform man- 

 ner, until, towards the fourth or sixth week, the whole is transformed 

 into a spongy, but firm osseous mass, investing the exterior of the 

 broken extremities, and extending between them in the form of a 

 case, by which they are firmly held together. If the medullary 

 canal has been broken across, and the broken ends evenly adjusted, 

 there will be likewise an interior stem of new bone connecting the 

 medullary canal of the fragments in the axis of the bone; the 

 opposed surfaces of the compact tissue being as yet ununited. Th< 

 callus, or new bone, thus formed, was termed by Dupuytren 



