PELVIS AND BONES OF THE LEGS OF BIKDS. 145 



loid cavity backwards, parallel with the ilium ; it some- 

 times coalesces, as in the swan, with both the ilium and 

 pubis at its distal end. 



The cotyloid cavity is incomplete behind, and is closed 

 there by ligament. The femur, 65, is a short, cylindrical, 

 almost straight bone ; the head is a small hemisphere, 

 presenting at its upper part a depression for the " round 

 ligament." The single large " trochanter" generally rises 

 above the articular eminence, and is continuous with the 

 outer side of the shaft. The orifice for the admission of 

 air is situated in the depression between the trochanter 

 and head. The distal end presents two condyles, the 

 inner one for the inner condyloid cavity of the tibia ; the 

 outer one for the outer cavity of the tibia and for the 

 fibula ; the outer condyle is produced into a semicircular 

 ridge, which passes between the tibia and fibula; this 

 ridge puts the outer elastic ligament on the stretch, when 

 the fibula is passing over the condyle, and the fibula is 

 pulled into a groove at the back of the condyle, with a 

 jerk, when in extreme flexion ; this spring-joint is well 

 exemplified in both the swan and water-hen. 



The proximal end of the tibia is divided into the two 

 shallow condyloid cavities above noticed: two ridges- are 

 extended from its upper and anterior surface: the 

 strongest of these is the "procnemial" ridge, and is 

 slightly bent outwards ; the shorter one on the outside of 

 this is the " ectocnemial" ridge; they are usually united 

 above by a transverse ridge, called "epicnemial" ridge; 

 this is developed into a long process in the divers, grebes, 

 and guillemots : a fibular ridge projects slightly from the 

 upper third of the tibia for junction with the fibula. The 

 distal end of the tibia forms a transverse pulley or troch- 

 lea, with the anterior borders produced. Above the fore 

 13 



