PRINCIPLES OP VETERINARY SURGERY 59.5 



The rachitic osseous tissue is not arranged in concentric 

 lamellae. It does not contain osteoplasts. The cellular bod- 

 ies enclosed in the calcified fibrous tissue have no anasto- 

 motic branches characteristic of normal bone cells. These 

 modifications are observed over the entire diaphysis. The 

 Haversian canals are dilated, filled with a cellular marrow 

 and lined with a fibrous zone. The medullary vessels are 

 numerous ; their walls are thin ; they bleed easily, and the 

 fibrous stroma is strewn with yellowish pigments, accumu- 

 lated in heaps. Besides this rachitic tissue (the osseous tis- 

 sue of Virchow and the spongy tissue of Guerin) can be 

 distinguished old osseous lamellje, arranged concentrically 

 and exhibiting osteoplasts. They are made thinner and are 

 partly re-absorbed by the mechanism of Howship's lacunse. 

 The modifications of the periosteum and of the medullary 

 canal are also interesting. The periosteum is thickened and 

 very vascular, and between it and the bone are elongated 

 connective tissue cells instead of medullary cells, and a 

 zone of rachitic tissue in which the tracts, instead of being 

 parallel to the long axis of the bone, are promiscuously ar- 

 ranged, perpendicularly, oblique, etc. The rachitic tissue 

 developed by the periosteum is similar in structure to that 

 of the diaphysis. In the medullary canal analogous modifi- 

 cations are observed. The marrow becomes fibrillary and 

 even fibrous, as if beneath the periosteum, and it is the seat 

 of a special calcification, which is only incomplete ossifica- 

 tion. In the midst of all this portions of normal bone, rec- 

 ognizable as lamellce and osteoplasts, are always found. 

 These parts are always softened by a process analogous 

 to that of a rarefying osteitis. 



The rachitic bones are easily fractured, but owing to 

 the thickness of the periosteum there is usually no displace- 

 ment (sub-periosteal fracture). They are repaired by a 

 layer of rachitic osseous tissue formed by the periosteunT 



