OSTEOLOGY OF BIRDS 79 



appears to be straight, but seeing it laterally shows it to be greatly 

 curved from one end to the other, the concavity being along the 

 front of the shaft. It is much scooped out anteriorly, just below 

 the articular end [fig. 31]. This is continued a short distance down 

 the shaft, trending towards the inner side. At its deepest part, 

 above, the bone is pierced from before, backward, by a single fora- 

 men. Below this, and rather to the outer side there is a small, 

 elongated, though prominent tubercle. Running down the front of 

 the shaft from a point on the periphery of the proximal end, op- 

 posite the middle of the external articular depression for the con- 

 dyle of the tibia, to the middle of the outer trochlea, there is a 

 rounded and pronounced crest, much like the tibial crest in some 

 vertebrates. 



The outer aspect of this bone is broad and flat, though carried 

 to a sharp edge above on the inner aspect proper. This latter side 

 is not as broad as the outer aspect. These two surfaces meet to 

 form the anterior crest described above. From between the hypo- 

 tarsial processes to the trochleae, the posterior surfaces of the shaft 

 are deeply and longitudinally grooved. 



The margins of this excavation are sharp throughout their extent, 

 being the posterior edges of the two surfaces described as the inner 

 and anterior and the outer surfaces, above. 



Upon the lower edge of the inner of these two margins we find 

 a well marked elongated facet, intended for the articulation of a 

 large sized metatarsal. This latter bone is of considerable size in 

 this harrier, and its distal trochlear surface is very broad, being 

 placed transversely on the bone. Above, it is so articulated as to 

 allow of considerable freedom of movement, being attached to the 

 tarsometatarsus in the most usual manner by ligament. This distal 

 end of the tarsometatarsus, that bears the trochlear facets, is much 

 expanded in a lateral direction, being gently convex from side to side 

 anteriorly, where it shows the usual foramen for the anterior tibial 

 artery. Behind, it shows an amount of concavity, from side to side, 

 equal to the convexity of the anterior aspect. The trochlear pro- 

 cesses for the pedal digits are separated by not very deep notches. 

 Their lower surfaces are about in the same plane, the inner one 

 perhaps being rather lower than either of the others, though not 

 noticeably so at first sight. 



The mid trochlea presents a deep median anteroposterior groove, 

 not well marked in either of the others. In comparing the hypo- 

 tarsial processes of the tarsometatarsus as they occur in Circus, 



