68 Transaction!^. — Zoology. 



The shaft in its nppei- portion is considerably bent backwards, and veiy 

 broad where it is attached to the tibia, after which it decreases rapidly in size. 

 Two shallow pits for the insertion of tendons are well marked. 



Metataksus. 

 Harpagornis moorei. PI. YII., Figs. 5 and 6. 



The following are the measvirements of this important bone : — 



Inches . 

 Totallength ... ... ... ... ... 6-08 



Circumference at its proximal end. the calcaneal ridges 



included ... ... ... ... ... 4-09 



Circumference at its distal end ... ... ... 4' 2 8 



Circumference of shaft where thinnest ... ... 1"90 



In its general form also, this bone resembles in its main features that of 

 Aquila, except being somewhat more robust. 



The shaft at its upper end is expanded and transversely flat, gradually 

 becoming narrower, and assuming towards its middle a trihedral shape, after 

 which it flattens again above the fore and aft canal, between the middle and 

 outer metatarsal, near their distal ends. 



In Circus the trihedral portion of the bone is much longer, even in 

 comparison to its whole length, than either in the fossil bone or in Aquila. 



The form and position of the trochlear condyles agi-ee more closely with 

 Circus, they being broader and with a larger space between them than in 

 Aquila. 



The tuberosity for the insertion of tibialis anticvis is remarkably developed, 

 another proof of the great power the fossil bird must have possessed. 



The ectocondylar concavity is well marked, far more than in the recent 

 species, in both of which the outer side of the proximal surface is almost plane. 



The three tendinal grooves between the calcaneal processes and the inner 

 posterior ridge are deeply excavated, much more than in Aquila audax. 

 Half-way down the shaft they unite to form one concave channel, which, 

 above and close to the process for the attachment of the metatarsal of the back 

 toe, runs out to a flat surface. 



The two fore and aft foramina in the upper part of the bone, in the grooves 

 near the base of the anterior intercondylar promiiiences, are well marked. 



The surface of the bone running from the outer mai-gin of the ectocondylar 

 ridge down to the outer condyle is very broad and flat, as in Aquila, having 

 its greatest diameter in the middle portion of the bone, thus forming the base 

 of its trihedral form. 



In Circus the base of the bone is situated moi'e in its postei'ior poi'tion, the 

 ridge running towards the centre of the anterior portion of the shaft, giving 

 the latter a triangular form for about two-thirds of its entire length. 



