326 THE VERTEBRATE SKELETON. 



the long narrow obturator foramen. Behind the ischium 

 the pubis is produced into a long curved downwardly-project- 

 ing process, and in front of the acetabulum it bears a short 

 blunt pectineal or pre-pubic process (fig. 61, 4) probably 

 homologous with the pre-pubis of Orthopod Dinosaurs. The 

 remainder of the pubis is homologous with the post-pubis of 

 Orthopod Dinosaurs. 



THE POSTERIOR LIMB. 



The leg of the bird is somewhat differently constructed from 

 that of other vertebrates owing to the fact that there is no 

 free tarsus, the proximal tarsals having fused with the tibia, 

 and the distal with the metatarsals. 



The thigh consists of a single bone, the femur. The femur 

 is a comparatively short bone with a straight shaft and ex- 

 panded ends. The proximal end bears on its inner side a 

 rounded head, which articulates with the acetabulum. On its 

 outer side is an irregular outgrowth, the great trochanter, 

 while between the two is the surface which meets the antitro- 

 chanter of the ilium. The posterior end also is expanded 

 and marked by a wide groove which lodges the patella. On 

 each side of the groove is a strong condylar ridge for articu- 

 lation with the tibia. The external condyle is deeply grooved 

 behind for articulation with the fibula. 



The crus or shin consists of two separate bones, (1) the 

 tibio-tarsus, formed by the fusion of the tibia with the proxi- 

 mal row of tarsals, and (2) the fibula. 



The tibio-tarsus is a thick straight bone nearly twice as 

 long as the femur. Both ends of the bone are considerably 

 expanded. The proximal end bears two slight depressions 

 which articulate with the condyles of the femur, and a third 

 depression which partly lodges the patella. The proximal end 

 of the anterior or extensor surface is drawn out into a very 

 prominent cnemial crest which bends over towards the post- 

 axial side of the bone ; a slight ridge is continued from it all 



