EICKETS. 55 



them that applied anatomy has mostly to deal. The disease 

 chiefly manifests itself in the epiphyses. Here the normal pro- 

 cess of intra-cartilaginous bone formation becomes perverted ; 

 the layer of proliferating cartilage becomes increased in breadth 

 and thickness, and the progress of ossification in it is imperfect 

 arid irregular. The characteristic thickening of the bones is due 

 to the presence of the imperfectly consolidated cartilage, and so 

 is found near, but not absolutely at the ends of the bones. In the 

 long bones the medullary canal also becomes enlarged, the hard 

 bone is absorbed, and soft spongy bone lying under thickened 

 periosteum takes its place. In estimating the evidence of rickets 

 it is well to bear in mind that the ends of the ribs, where they 

 join their cartilages, are normally slightly enlarged. 



The deformities of rickets are produced in various ways. Many 

 are the results of attitude and pressure, some are due to muscular 

 action, and others are caused by atmospheric pressure acting in 

 conjunction with impeded inspiration. 



Deformities due to attitude may often be seen in the lower ends 

 of the tibiae and in the chest. They may also occur at the lower end 

 of the femur. Children who have not learned to walk often lie or 

 sit with the lower ends of the tibiae crossing each other ; the ends 

 of these bones then become bent by mutual pressure, and the 

 curve of one bone fits accurately the curve in the other. The 

 tendency of young children with rickets to lie with the forearms 

 flexed over the front of the chest accounts for the presence of a 

 longitudinal sulcus at the side of the thorax into which the upper 

 arm fits, and which at its lower end is often prolonged obliquely 

 forwards and upwards, corresponding to the position of the fore- 

 arm. It is believed that a bending inwards of the lower end of 

 the femur produced by sitting or lying with the knees crossed is 

 the basis of some cases of knock-knee, whilst in other cases the 

 lower end of the femur may become so twisted on the shaft that 

 the knee points outwards. 



In children who have learned to walk, an exaggeration of the 

 normal forward bend of the tibia in its lower parts may be pro- 

 duced ; the weak point of the bone is at the junction of the 



