52 ANATOMY OF THE DOMESTIC FOWL 



becomes more flattened. The inner side of the inner condyle is 

 flattened and is provided with a tuberosity at its mid-part and a 

 second just above the posterior part of the condyle. 



The outer condyle is formed in the same manner as the inner con- 

 dyle. It is indented at its broad, lower end by an angular groove, 

 which, winding divides the posterior part of the condyle into two 

 convexities. The more external .convex ridge and the groove di- 

 viding it from the outer condyle are_adapted to the head of the fibula. 

 There is in this part a. fibular ridge and above this ridge a tuberosity. 



The Tibia. Location. — The tibia (Fig. 12, D and C) extends ob- 

 liquely downward and backward from the knee-joint to the hock. 

 It articulates above with the femur and, by its procnemial process 

 with the patella, below with the metatarsus, and laterally with the 

 fibula. 



Description. — The tibia is the longest bone in the posterior limb, 

 and possesses a shaft and two extremities. It is largest at the proxi- 

 mal end and presents three faces. 



The proximal extremity presents a semi-oval articular surface, 

 not quite at right angles with the shaft, which articulates with the 

 condyles of the femur. The margin is raised toward the anterior 

 of the bone. The head of the tibia, or caput tibicB, extends into a 

 rotular process which extends transversely, and is truncate. From 

 the anterior of this process there descends two vertical ridges; one 

 near the angle of the rotular process, the procnemial ridge; the other 

 from the outer fibular angle, the ectocnemial ridge. On the outer side 

 of the intercondyla:r tuberosity there is a surface for the ligamentous 

 union with the head, of the fibula; and a short distance below this 

 there is a vertical ridge for the close attachment, almost a fusion, 

 with the fibula, called the. fibular ridge. 



The shaft, or corpus tibice is straight and the upper two-thirds 

 sub trihedral; the lower third oval. A nutrient foramen occurs near 

 the upper postero-internal portion of the middle third of the 

 bone. 



The distal extremity is much smaller than the proximal one; 

 it is quadrangular in form. The expanded inferior end of the tibia 

 forms two articular condyles above which posteriorly there is the 

 epicondyloid fossa. The inner condyle, the larger, has a groove near 

 the lower end of the anterior part of the shaft, which deepens to- 

 ward the intercondyloid space. This intercondyloid fossa in young 

 birds is covered by a strong ligament, which in older birds, becomes 



