592 



PRINCIPLES OF VETERINARY SURGERY . 



penetrate into the diaphyseal bone. In order to understand 

 thoroughly the histological lesions of rickets the mechan- 

 ism of normal ossification must be understood. Bones grow 

 from the simultaneous operations of the cartilage of conju- 

 gation, the periosteum and the marrow. A section through 

 the cartilage shows that near the line of ossification, the 

 cartilaginous cells are arranged in a series of lines, separated 

 by zones of hyaline substance. The cells multiply, new ele- 

 ments appear with separate capsules and enveloped in groups 



Fig. 92. 

 Zone of Proliferation of a Rachitic Epiphyseal Cartilage (SOO Diameters), 

 (a) Unossified Cellular Columns, (b) Medullary Spaces of Carti- 

 laginous Tissue in Course of Ossification. 



with a large common capsule. These capsules are then 

 dissolved and the spaces are filled with round cells without 

 capsules. These are medullary spaces. Vessels penetrate 

 to them and some of the round cells are transformed into 

 osteoblasts, which secrete the osseous lamella from the cir- 

 cumferences to the centers of the medullary spaces, and 

 then send out canaliculate and anastomotic extensions to 

 become osteoplasts. 



On section of the rachitic bone this progressive evolu- 

 tion, which ends in substitution of the cartilage, is markedly 



