174 ENCHONDROMATA. 



less possesses tlie most substantial claim on our notice on the 

 ground of its morphological constitution. I allude to that 

 peculiar sort of connective substance (Bindesubstanz) which is 

 called true bone after it has been impregnated with calcareous 

 saltSj but which, before this impregnation, consists of a highly- 

 refracting, dense and homogeneous matrix, in which the future 

 bone-lacuna still exhibit more of a rounded or rather perhaps of a 

 polygonal form, with very short processes. The trabeculas of an 

 osteophyte {see Diseases of Bone) are composed of this tissue ; in 

 thin layers, it lines the medullary spaces of such bones as are 

 passing from the spongy to the compact state. It plays a great 

 part in the repair of fractures by forming the main bulk of what 

 is known as " callus." Its truly cartilaginous properties are 

 however especially manifest when, as in the osteoid-chondro- 

 mata, it forms tumours, often of colossal size. 



^ 140. Osteoid cartilage may also originate independently of 

 the bones : in a compound tumour from the back, Virchow found 

 portions of well-marked osteoid cartilage side by side with 

 myxomatous and lipomatous elements ; but as a general rule 

 such tumours spring from bone. Their growth begins between 

 the periosteum and the surface of the bone, but they sub- 

 sequently penetrate through both the periosteum and the 

 compact cortex. They usually present themselves as fusi- 

 form or pear-shaped swellings of one of the extremities of a 

 long (tubular) bone. They have been most often met with in 

 the humerus and femur. Retrograde metamorphoses are less 

 common in these than in any other of the heteroplastic tumours 

 which we have hitherto considered. This immunity is connected 

 with the very complete and uniformly efficient vascularisation of 

 every part of the tumour, an advantage which the osteoid- 

 chondroma enjoys in common with osteophytes and callus. The 

 cartilaginous trabecule of the osteoid substance form a delicate 

 framework, in whose meshes even the finest capillaries are free 

 from all risk of being squeezed by the growing tissue. One 

 metamorphosis only, and one which might be anticipated a priori, 

 is met with in nearly every osteoid-chondroma ; I mean a transi- 

 tion of its proper tissue into that of true bone. Hence it is that 

 an osteoid-chondroma creaks under the knife, and that we are 

 sometimes obliged to have recourse to the saw in order to divide 

 it. The ossified portions are known at once on the cut surface 



