PATELLA. 747 



internal and posterior. The external gives origin to the 

 peronei muscles. The internal is divided by a ridge to 

 which the interosseous ligament is attached ; and the sur- 

 face in front of the ridge is for the origin of the extensor 

 muscles; that behind the ridge for the tibialis posticus. 

 The posterior surface is covered by the soleus, and below 

 by the flexor pollicis pedis. 



The superior extremity or head is circular and small, and 

 presents a slight cavity for articulating with the external 

 head of the tibia. Its outer surface gives attachment to 

 the external lateral ligament and tendon of the biceps 

 muscle. The inferior or tarsal extremity is larger than 

 the upper, and ends in a long, oval projection, termed the 

 external malleolus. This process internally is smooth and 

 triangular for articulating with the astragalus; a little 

 above it is rough for connecting with the tibia ; posteriorly 

 it is grooved for the tendons of the peronei muscles ; exte- 

 riorly it is rough and superficial and gives attachment to 

 ligaments. The centre of the shaft contains the nutritious 

 foramen. 



The structure is the same as that of the tibia, being 

 compact in its shaft and cellular in its extremities. 



Its development is by three points ; one for the shaft, and 

 one for each extremity. Ossification begins soon after it 

 does in the tibia; during the second year the lower epiph- 

 ysis begins to ossify, and in the fourth or fifth year the 

 upper epiphysis, the bone being completed about the 

 twenty-fifth year. The fibula is articulated with the tibia 

 and astragalus. 



The patella or rotula is situated in front of 

 the knee joint, and is regarded as a sesamoid 

 bone, developed in the tendon of the exten- 

 sor femoris muscle. Its shape is triangular ; 

 its base above receives the tendons of the 

 extensor muscles ; its apex below is pointed, 



FIG. 242 represents the Patella, a 6 Point of attachment of the tendon of 

 the triceps-extensor and femoris muscle, c Point of attachment of the liga- 

 mentum patella. 



