OSTEOLOGY ' . . . 53 



ossified. On the lateral side of each condyle, there is a depression 

 for the attachment of ligaments. 



The Patella. Location. The patella, or knee-cap, thin and wide, 

 articulates with the procnemial process of the tibia, and with, the 

 deep trochlea of the distal end of the femur. 



Description. The patella is irregular in shape with three faces 

 and three borders. The posterior surface is articular. The other 

 two surfaces are rough for tendinous attachment. The patellar 

 ligaments in old birds may become ossified. 



In order to turn the foot in and out, the tibia not only turns 

 around the inner condyle of the femur, but also around the patella, 

 so that the posterior surface turns outward and thus turns outward 

 the metatarsus and all the toes. 



The Fibula. Location. The fibula lies at the outer border of the 

 tibia. It articulates superiorly with the outer condyle of the femur, 

 and laterally with the tibia. 



Description. The fibula is rudimentary; it is largest superiorly and 

 tapers to a slender point. The head is compressed laterally, and fur- 

 nishes an upper and an inner articular surface. 



The Tarsus. There exist, during fetal development of the chick, 

 two rows of tarsal bones which later become fused. The upper 

 row fuses with the tibia and the lower with the metatarsus. There- 

 fore, in the adult, there is no tarsus. 



The Metatarsus. Location. The metatarsal bone extends down- 

 ward and forward. In birds it consists of one bone, which ar- 

 ticulates superiorly with the inferior extremity of the tibia. On the 

 distal end it has a threefold trochlear arrangement which articulates 

 with the three principal digits. 



Description. The proximal extremity posteriorly has a process 

 which may be considered as a consolidation of originally separate 

 metatarsal bones. The process at the supero-posterior part of 

 the metatarsus is called the hypotarsus of the tarso-metatarsus, 

 through which extends a canal called the hypotarsal canal, and which 

 gives passage to flexor tendons. 



The proximal end of the metatarsus is ossified from one center of 

 ossification forming an epiphysis which caps the ends of the three 

 original metatarsal bones that coalesce, first with one another, then 

 with the epiphysis, thus forming a single compound bone. Above 

 and just to the inside of the metatarsus there may occur a small 

 bone which is imbedded in ligaments and articulates with the 



