THE PATELLA OR ROTDLA. 209 



of the leg are sometimes united by anchylosis at their lower 

 ends. 



The principal use of this bone is to afford origin arvd inser- 

 tion to muscles ; and to give a particular direction to their 

 tendons. It likewise assists to make the articulation of the 

 foot more secure and firm, and to complete the hinge-like joint 

 at the ankle. The ends of the tibia and fibula being larger 

 than their middle, a space is here left, which is filled up with 

 a ligament similar to that which is extended between the 

 bones of the forearm ; and which is also discontinued at its 

 upper part, where the tibialis anticus immediately adheres to 

 the solaeus and tibialis posticus j but every where else k gives 

 origin to muscular fibres. 



The Patella or Rotula 



Is a small flat bone situated at the forepart of the joint of 

 the knee. Its shape resembles the common figure of the heart 

 with its point downwards. The anterior convex surface of 

 the rotula is pierced by a great number of holes, into which 

 are inserted the fibres of the strong ligament that is spread over 

 it. Its posterior surface is smooth, covered with a cartilage, 

 and divided by a middle convex ridge into two cavities, of 

 which the external is the largest ; and both are exactly adapted 

 to the pulley of the os femoris, on which they are placed in the 

 most ordinary unstraining postures of the legs : but, when the 

 leg is much bent, the patella descends far down on the condyles ; 

 and when the leg is fully extended, the patella rises higher in 

 its upper part than the pulley of the thigh bone. The plane 

 smooth surface is surrounded by a rough prominent edge, to 

 which the capsular ligament adheres. Below, the point of the 

 bone is scabrous, where the strong tendinous ligament from the 

 tubercle of the tibia is fixed. The upper horizontal part of this 

 bone is flattened and unequal where the tendons of the exten- 

 sors of the leg are inserted. 



The substance of the patella is cellular, with very thin firm 

 external plates ; but then these cells are so small and such a 

 quantity of bone is employed in their formation, that scarce 

 18* 



