OSTEOLOGY OF BIRDS 1 23. 



does not rise above the summit of the ibone. The shaft is stout 

 and quite devoid of any marked curvature; the condylar extremity 

 being characterized by its very deep popliteal fossa, and by the in- 

 ternal condyle throwing partly across it a bluntly rounded process. 

 All this is very different as compared with what we find in the 

 femur of such a bird as the White-headed eagle ; nor does it espe- 

 cially agree with any of our ordinary accipitrine birds. 



Some excellent characters are seen in the tibio tar sits and fibula 

 of the osprey. With respect to the former it is seen to be nearly 

 straight from end to end, only the lower portion of the bone being 

 very slightly curved to the front. At the proximal end a slight 

 lateral compression of the head of the bone is evident, and the 

 cnemial processes are considerably reduced in size. The ridge 

 at the outer side of the shaft for the fibular articulation, the 

 fibular ridge, is long, and below this an anteroposterior flattening of 

 the shaft becomes more evident as we approach the condylar ex- 

 tremity. Above the condyles in front a very deep fossa exists, and 

 this is obliquely spanned across by a single osseous bridgelet, the 

 lower end of which is over the external condyle. To the outer side 

 of this latter point a prominent little tubercle is ever present. Dif- 

 fering with the eagles, we find here in Pandion that the condyles to 

 this bone are as jutting and prominent posteriorly, as they are in 

 front, and the intercondylar notch is deep all the way round. 



The fibula is complete, only being coossified with the tibiotarsus 

 at its distal end. Its lower half is ribbonlike, though' strong, and 

 is longitudinally grooved and quite straight. 



Tarso metatarsus is short, strong, and straight, being flattened,. 

 in so far as its shaft is concerned, in the anteroposterior direction. 

 Its hypotarsus is large and distinct, in one piece, and exhibits a 

 median vertical perforation for the passage of tendons, of some 

 considerable size. Just below the head of the bone, on the anterior 

 aspect of the shaft, the inner half of the same has fused upon it a 

 strong little osseous cylindrical span for the confinement of tendons, 

 such as we see in owls. To its outer side occur the two perforating 

 foramina, close together. Below these, and directly in the middle 

 of the shaft, is the large tubercle for the insertion of the tendon of 

 the tibialis anticus muscle. At the distal end, the trochleae are 

 prominent and large, the lateral ones curving much to the rear. 

 The foramen for the anterior tibial artery is also unusually sizable. 



Great strength and no mean size likewise stamp the free first 

 metatarsal, which is articulated in the usual manner with the main 

 shaft of the bone. 



